Californians are paying an average of $4.668 a gallon, the highest price in the nation. Many motorists are paying over $5.
Feinstein says that paying hundreds of dollars every time you fill your tank is unthinkable. For the second time in the last few months, the California Democrat has sent a letter to the Federal Trade Commission asking for an immediate probe.
She also asked in August when gas was 45 cents cheaper.
Gov. Jerry Brown over the weekend ordered state smog regulators to allow winter-blend gas to be sold three weeks early in the state.
Experts are predicting prices will climb to $4.85 before coming down.