diff --git a/src/seth/CHANGELOG.md b/src/seth/CHANGELOG.md
index 4b2ea6403..24aaa460a 100644
--- a/src/seth/CHANGELOG.md
+++ b/src/seth/CHANGELOG.md
@@ -15,6 +15,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `seth index` command returns the slot number for the specified mapping type and input data
 - `seth --from-fix` command converts fixed point numbers into parsed integers with the specified number of decimals
 - `seth run-tx` now fetches contract source from etherscan if `ETHERSCAN_API_KEY` is set
+- `seth mktx` now estimates gas limit if `ETH_GAS` is not set
+- `seth send` now estimates gas limit if `ETH_GAS` is not set
 
 ### Fixed
 
diff --git a/src/seth/README.md b/src/seth/README.md
index 2e52b1202..0786eae9c 100644
--- a/src/seth/README.md
+++ b/src/seth/README.md
@@ -238,7 +238,6 @@ wei—the smallest possible amount of ether—to the [Ethereum
 Foundation's donation address]:
 
     $ seth send --value 1 0xfB6916095ca1df60bB79Ce92cE3Ea74c37c5d359
-    seth-send: warning: `ETH_GAS' not set; using default gas amount
     Ethereum account passphrase (not echoed):
     seth-send: Published transaction with 0 bytes of calldata.
     seth-send: 0xe428d4bb148ded426777ae892578507e4f394f608ad9d3a9d0229e8348ba72e3
@@ -660,6 +659,7 @@ node's gas estimation.
     seth estimate [<options>] <to> <sig> [<args>]
     seth estimate [<options>] --create <code> <sig> [<args>]
     seth estimate [<options>] --create <code> <data>
+    seth estimate [<options>] --create <data>
 
 Options are similar to [`seth send`], but no transaction is published.
 
@@ -829,7 +829,7 @@ Sign and publish a transaction to the blockchain.
 | ------------- | --------------- | ------------ | ---------------                   |
 | `--block`     | `ETH_BLOCK`     | `latest`     | block number                      |
 | `--from`      | `ETH_FROM`      | n/a          | sender                            |
-| `--gas`       | `ETH_GAS`       | `200000`     | gas quantity                      |
+| `--gas`       | `ETH_GAS`       | estimated    | gas quantity                      |
 | `--gas-price` | `ETH_GAS_PRICE` |              | gas price                         |
 | `--prio-fee`  | `ETH_PRIO_FEE`  |              | EIP-1559 priority fee (miner tip) |
 | `--value`     | `ETH_VALUE`     | `0`          | ether value                       |
diff --git a/src/seth/libexec/seth/seth-estimate b/src/seth/libexec/seth/seth-estimate
index 41864607e..26e03fd5e 100755
--- a/src/seth/libexec/seth/seth-estimate
+++ b/src/seth/libexec/seth/seth-estimate
@@ -4,6 +4,7 @@
 ###    or: seth estimate [<options>] <receiver> <data>
 ###    or: seth estimate [<options>] --create <code> <sig> [<args>]
 ###    or: seth estimate [<options>] --create <code> <data>
+###    or: seth estimate [<options>] --create <data>
 ###
 ### Perform a local call to <receiver> and return the gas usage.
 ###
@@ -15,7 +16,7 @@
 ### With `-F <sender>', simulate calling <receiver> from <sender>
 ### With `-V <value>', simulate transferring <value> to <receiver>.
 set -e
-[[ $2 ]] || seth --fail-usage "$0"
+[[ $1 ]] || seth --fail-usage "$0"
 
 if [[ $SETH_CREATE ]]; then
   DATA=$(seth --to-hexdata "$1")
diff --git a/src/seth/libexec/seth/seth-mktx b/src/seth/libexec/seth/seth-mktx
index d5790b27e..b9a340fdd 100755
--- a/src/seth/libexec/seth/seth-mktx
+++ b/src/seth/libexec/seth/seth-mktx
@@ -13,20 +13,34 @@ if [[ $2 ]]; then
   data=$(seth calldata "${@:2}")
 fi
 
+data=${data:-0x}
+
+if [[ -z "$SETH_CREATE" ]]; then
+  TO=$(seth --to-address "$1")
+fi
+
+if [[ -z "$ETH_GAS" ]]; then
+  if [[ $SETH_CREATE ]]; then
+    ETH_GAS=$(seth estimate --create $data)
+  else
+    ETH_GAS=$(seth estimate $TO $data)
+  fi
+fi
+
 args=(
   --from "$(seth --to-address "$ETH_FROM")"
   --nonce "${ETH_NONCE:-$(seth nonce "$ETH_FROM")}"
   --chain-id "$(seth chain-id)"
   --gas-price "${ETH_GAS_PRICE:-$(seth gas-price)}"
-  --gas-limit "${ETH_GAS:-200000}"
+  --gas-limit "$ETH_GAS"
   --value "$value"
-  --data "${data:-0x}"
+  --data "$data"
 )
 
 if [[ $SETH_CREATE ]]; then
   args+=(--create)
 else
-  args+=(--to "$(seth --to-address "$1")")
+  args+=(--to "$TO")
 fi
 
 if [[ $ETH_PRIO_FEE ]]; then
diff --git a/src/seth/libexec/seth/seth-send b/src/seth/libexec/seth/seth-send
index f12300de7..3d72f1b5d 100755
--- a/src/seth/libexec/seth/seth-send
+++ b/src/seth/libexec/seth/seth-send
@@ -23,8 +23,6 @@ set -e
 
 [[ $ETH_FROM ]] ||
 seth --fail "${0##*/}: error: \`ETH_FROM' not set; send from which account?"
-[[ $ETH_GAS ]] ||
-echo >&2 "${0##*/}: warning: \`ETH_GAS' not set; using default gas amount"
 if [[ $SETH_RESEND ]]; then
   nonce=$(seth nonce "$ETH_FROM")
   export ETH_NONCE=$nonce
@@ -44,9 +42,18 @@ else
   fi
 fi
 
+if [[ -z "$ETH_GAS" ]]; then
+  if [[ $SETH_CREATE ]]; then
+    ETH_GAS=$(seth estimate --create $DATA)
+  else
+    ETH_GAS=$(seth estimate $TO ${DATA:-0x})
+  fi
+fi
+
 jshon+=(-n {})
 [[ $TO ]] && jshon+=(-s "$TO" -i to)
 [[ $DATA ]] && jshon+=(-s "$DATA" -i data)
+[[ $ETH_GAS ]] && jshon+=(-s "$ETH_GAS" -i gas)
 # shellcheck disable=SC2207
 jshon+=($(seth --send-params))
 jshon+=(-i append)