diff --git a/hist/hist/src/TGraph.cxx b/hist/hist/src/TGraph.cxx
index 9d8ee9ff1fbe9..2d5b362d58d88 100644
--- a/hist/hist/src/TGraph.cxx
+++ b/hist/hist/src/TGraph.cxx
@@ -358,12 +358,13 @@ TGraph::TGraph(const TH1 *h)
       Error("TGraph", "Histogram must be 1-D; h %s is %d-D", h->GetName(), h->GetDimension());
       fNpoints = 0;
    } else {
-      fNpoints = ((TH1*)h)->GetXaxis()->GetNbins();
+      fNpoints = h->GetXaxis()->GetNbins();
    }
 
-   if (!CtorAllocate()) return;
+   if (!CtorAllocate())
+      return;
 
-   TAxis *xaxis = ((TH1*)h)->GetXaxis();
+   auto xaxis = h->GetXaxis();
    for (Int_t i = 0; i < fNpoints; i++) {
       fX[i] = xaxis->GetBinCenter(i + 1);
       fY[i] = h->GetBinContent(i + 1);
@@ -440,6 +441,7 @@ TGraph::TGraph(const TF1 *f, Option_t *option)
 /// The string format is by default `"%lg %lg"`.
 /// This is a standard c formatting for `scanf()`.
 /// For example, set format to  `"%lg,%lg"` for a comma-separated file.
+/// If format string is empty, suitable value will be provided based on file extension
 ///
 /// If columns of numbers should be skipped, a `"%*lg"` or `"%*s"` for each column
 /// can be added,  e.g. `"%lg %*lg %lg"` would read x-values from the first and
@@ -473,11 +475,21 @@ TGraph::TGraph(const char *filename, const char *format, Option_t *option)
    std::string line;
    Int_t np = 0;
 
-   // No delimiters specified (standard constructor).
-   if (strcmp(option, "") == 0) {
+   TString format_ = format;
+
+   if (!option || !*option) { // No delimiters specified (standard constructor).
+      // is empty format string specified - try to guess format from the file extension
+      if (format_.IsNull()) {
+         if (fname.EndsWith(".txt", TString::kIgnoreCase))
+            format_ = "%lg %lg";
+         else if (fname.EndsWith(".tsv", TString::kIgnoreCase))
+            format_ = "%lg\t%lg";
+         else
+            format_ = "%lg,%lg";
+      }
 
       while (std::getline(infile, line, '\n')) {
-         if (2 != sscanf(line.c_str(), format, &x, &y)) {
+         if (2 != sscanf(line.c_str(), format_.Data(), &x, &y)) {
             continue; //skip empty and ill-formed lines
          }
          SetPoint(np, x, y);
@@ -489,7 +501,6 @@ TGraph::TGraph(const char *filename, const char *format, Option_t *option)
    } else {
 
       // Checking format and creating its boolean counterpart
-      TString format_ = TString(format) ;
       format_.ReplaceAll(" ", "") ;
       format_.ReplaceAll("\t", "") ;
       format_.ReplaceAll("lg", "") ;
diff --git a/hist/hist/src/TGraphAsymmErrors.cxx b/hist/hist/src/TGraphAsymmErrors.cxx
index f7563d7984689..da28524750736 100644
--- a/hist/hist/src/TGraphAsymmErrors.cxx
+++ b/hist/hist/src/TGraphAsymmErrors.cxx
@@ -289,6 +289,8 @@ TGraphAsymmErrors::TGraphAsymmErrors(const TH1* pass, const TH1* total, Option_t
 ///  - format = `"%lg %lg %lg %lg"` read only 4 first columns into X, Y, EYL, EYH
 ///  - format = `"%lg %lg %lg %lg %lg %lg"` read only 6 first columns into X, Y, EXL, EXH, EYL, EYH
 ///
+/// If format string is empty, suitable value will be provided based on file extension
+///
 /// For files separated by a specific delimiter different from ' ' and `\\t` (e.g. `;` in csv files)
 /// you can avoid using `%*s` to bypass this delimiter by explicitly specify the `option` argument,
 /// e.g. `option=" \\t,;"` for columns of figures separated by any of these characters (`' ', '\\t', ',', ';'`)
@@ -314,18 +316,30 @@ TGraphAsymmErrors::TGraphAsymmErrors(const char *filename, const char *format, O
    std::string line;
    Int_t np = 0;
 
-   if (strcmp(option, "") == 0) { // No delimiters specified (standard constructor).
+   TString format_ = format;
+
+   if (!option || !*option) {  // No delimiters specified (standard constructor).
+
+      Int_t ncol = 6;
+      if (format_.IsNull()) {
+         if (fname.EndsWith(".txt", TString::kIgnoreCase))
+            format_ = "%lg %lg %lg %lg %lg %lg";
+         else if (fname.EndsWith(".tsv", TString::kIgnoreCase))
+            format_ = "%lg\t%lg\t%lg\t%lg\t%lg\t%lg";
+         else
+            format_ = "%lg,%lg,%lg,%lg,%lg,%lg";
+      } else
+         ncol = TGraphErrors::CalculateScanfFields(format);  //count number of columns in format
 
-      Int_t ncol = TGraphErrors::CalculateScanfFields(format);  //count number of columns in format
       Int_t res;
       while (std::getline(infile, line, '\n')) {
          exl = exh = eyl = eyh = 0.;
          if (ncol < 3) {
-            res = sscanf(line.c_str(), format, &x, &y);
+            res = sscanf(line.c_str(), format_.Data(), &x, &y);
          } else if (ncol < 5) {
-            res = sscanf(line.c_str(), format, &x, &y, &eyl, &eyh);
+            res = sscanf(line.c_str(), format_.Data(), &x, &y, &eyl, &eyh);
          } else {
-            res = sscanf(line.c_str(), format, &x, &y, &exl, &exh, &eyl, &eyh);
+            res = sscanf(line.c_str(), format_.Data(), &x, &y, &exl, &exh, &eyl, &eyh);
          }
          if (res < 2) {
             continue; //skip empty and ill-formed lines
@@ -339,7 +353,6 @@ TGraphAsymmErrors::TGraphAsymmErrors(const char *filename, const char *format, O
    } else { // A delimiter has been specified in "option"
 
       // Checking format and creating its boolean equivalent
-      TString format_ = TString(format) ;
       format_.ReplaceAll(" ", "") ;
       format_.ReplaceAll("\t", "") ;
       format_.ReplaceAll("lg", "") ;
diff --git a/hist/hist/src/TGraphErrors.cxx b/hist/hist/src/TGraphErrors.cxx
index c8b257b360b6f..f9f3047a6489c 100644
--- a/hist/hist/src/TGraphErrors.cxx
+++ b/hist/hist/src/TGraphErrors.cxx
@@ -223,6 +223,8 @@ TGraphErrors::TGraphErrors(const TH1 *h)
 ///   - format = `"%lg %lg %lg"` read only 3 first columns into X,Y and EY
 ///   - format = `"%lg %lg %lg %lg"` read only 4 first columns into X,Y,EX,EY.
 ///
+/// If format string is empty, suitable value will be provided based on file extension
+///
 /// For files separated by a specific delimiter different from ' ' and `\\t` (e.g. `;` in csv files)
 /// you can avoid using `%*s` to bypass this delimiter by explicitly specify the `option` argument,
 /// e.g. `option=" \\t,;"` for columns of figures separated by any of these characters (`' ', '\\t', ',', ';'`)
@@ -248,18 +250,30 @@ TGraphErrors::TGraphErrors(const char *filename, const char *format, Option_t *o
    std::string line;
    Int_t np = 0;
 
-   if (strcmp(option, "") == 0) { // No delimiters specified (standard constructor).
+   TString format_ = format;
+
+   if (!option || !*option) {  // No delimiters specified (standard constructor).
+
+      Int_t ncol = 4;
+      if (format_.IsNull()) {
+         if (fname.EndsWith(".txt", TString::kIgnoreCase))
+            format_ = "%lg %lg %lg %lg";
+         else if (fname.EndsWith(".tsv", TString::kIgnoreCase))
+            format_ = "%lg\t%lg\t%lg\t%lg";
+         else
+            format_ = "%lg,%lg,%lg,%lg";
+      } else
+         ncol = CalculateScanfFields(format);  //count number of columns in format
 
-      Int_t ncol = CalculateScanfFields(format);  //count number of columns in format
       Int_t res;
       while (std::getline(infile, line, '\n')) {
          ex = ey = 0;
          if (ncol < 3) {
-            res = sscanf(line.c_str(), format, &x, &y);
+            res = sscanf(line.c_str(), format_.Data(), &x, &y);
          } else if (ncol < 4) {
-            res = sscanf(line.c_str(), format, &x, &y, &ey);
+            res = sscanf(line.c_str(), format_.Data(), &x, &y, &ey);
          } else {
-            res = sscanf(line.c_str(), format, &x, &y, &ex, &ey);
+            res = sscanf(line.c_str(), format_.Data(), &x, &y, &ex, &ey);
          }
          if (res < 2) {
             continue; //skip empty and ill-formed lines
@@ -273,7 +287,6 @@ TGraphErrors::TGraphErrors(const char *filename, const char *format, Option_t *o
    } else { // A delimiter has been specified in "option"
 
       // Checking format and creating its boolean equivalent
-      TString format_ = TString(format) ;
       format_.ReplaceAll(" ", "") ;
       format_.ReplaceAll("\t", "") ;
       format_.ReplaceAll("lg", "") ;
diff --git a/hist/hist/test/test_TGraph_SaveAs.cxx b/hist/hist/test/test_TGraph_SaveAs.cxx
index 62386bb0c664e..8b56208ae8358 100644
--- a/hist/hist/test/test_TGraph_SaveAs.cxx
+++ b/hist/hist/test/test_TGraph_SaveAs.cxx
@@ -26,7 +26,7 @@ TEST(TGraphsa, SaveGraphAsCSV)
 
    gr.SaveAs("graph.csv");
 
-   auto gr1 = new TGraph("graph.csv", "%lg,%lg");
+   auto gr1 = new TGraph("graph.csv", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -42,7 +42,7 @@ TEST(TGraphsa, SaveGraphAsTSV)
 
    gr.SaveAs("graph.tsv");
 
-   auto gr1 = new TGraph("graph.tsv", "%lg\t%lg");
+   auto gr1 = new TGraph("graph.tsv", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -57,7 +57,7 @@ TEST(TGraphsa, SaveGraphAsTXT)
 
    gr.SaveAs("graph.txt");
 
-   auto gr1 = new TGraph("graph.txt", "%lg %lg");
+   auto gr1 = new TGraph("graph.txt", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -72,7 +72,7 @@ TEST(TGraphsa, SaveGraphErrorsAsCSV)
 
    gr.SaveAs("grapherrors.csv", "asroot"); // << asroot important for order of values
 
-   auto gr1 = new TGraphErrors("grapherrors.csv", "%lg,%lg,%lg,%lg");
+   auto gr1 = new TGraphErrors("grapherrors.csv", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -90,7 +90,7 @@ TEST(TGraphsa, SaveGraphErrorsAsTSV)
 
    gr.SaveAs("grapherrors.tsv", "asroot"); // << asroot important for order of values
 
-   auto gr1 = new TGraphErrors("grapherrors.tsv", "%lg\t%lg\t%lg\t%lg");
+   auto gr1 = new TGraphErrors("grapherrors.tsv", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -107,7 +107,7 @@ TEST(TGraphsa, SaveGraphErrorsAsTXT)
 
    gr.SaveAs("grapherrors.txt", "asroot"); // << asroot important for order of values
 
-   auto gr1 = new TGraphErrors("grapherrors.txt", "%lg %lg %lg %lg");
+   auto gr1 = new TGraphErrors("grapherrors.txt", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -125,7 +125,7 @@ TEST(TGraphsa, SaveGraphAsymmErrorsAsCSV)
 
    gr.SaveAs("graphasymmrrors.csv", "asroot"); // << asroot important for order of values
 
-   auto gr1 = new TGraphAsymmErrors("graphasymmrrors.csv", "%lg,%lg,%lg,%lg,%lg,%lg");
+   auto gr1 = new TGraphAsymmErrors("graphasymmrrors.csv", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -145,7 +145,7 @@ TEST(TGraphsa, SaveGraphAsymmErrorsAsTSV)
 
    gr.SaveAs("graphasymmrrors.tsv", "asroot"); // << asroot important for order of values
 
-   auto gr1 = new TGraphAsymmErrors("graphasymmrrors.tsv", "%lg\t%lg\t%lg\t%lg\t%lg\t%lg");
+   auto gr1 = new TGraphAsymmErrors("graphasymmrrors.tsv", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -164,7 +164,7 @@ TEST(TGraphsa, SaveGraphAsymmErrorsAsTXT)
 
    gr.SaveAs("graphasymmrrors.txt", "asroot"); // << asroot important for order of values
 
-   auto gr1 = new TGraphAsymmErrors("graphasymmrrors.txt", "%lg %lg %lg %lg %lg %lg");
+   auto gr1 = new TGraphAsymmErrors("graphasymmrrors.txt", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {
@@ -183,7 +183,7 @@ TEST(TGraphsa, SaveGraphAsymmErrorsAsOnlyErrorsCSV)
 
    gr.SaveAs("graphasymmrrors_reduce.csv", "asroot errors"); // << asroot important for order of values
 
-   auto gr1 = new TGraphErrors("graphasymmrrors_reduce.csv", "%lg,%lg,%lg,%lg");
+   auto gr1 = new TGraphErrors("graphasymmrrors_reduce.csv", "");
    EXPECT_EQ(gr1->GetN(), NP);
 
    for (int n = 0; n < NP; ++n) {