The trucks were carrying oil for NATO troops in Afghanistan.
The early-morning attack by more than two dozen militants occurred outside Peshawar, capital of Khyber Pakhtunkhwa province, scene of other attacks in recent months. The province was formerly known as the North-West Frontier province.
CNN, quoting senior police official Imtiaz Shah, reported the militants, carrying automatic weapons, first killed two security workers at the main gate of a terminal, where 18 tankers had been parked.
The attackers later killed two drivers sleeping in the terminal before setting off explosives they had planted under several tankers, the report said.
Two other drivers in the terminal were injured, Shah said.
There was no immediate claim of responsibility, CNN said.