Two major investment banks are warning U.S. consumers to enjoy falling gas prices while they can.

Goldman Sachs and J.P. Morgan Chase say oil prices will start rising again, leading to $5 per gallon gas.

The two most influential oil traders in the world are predicting the price of crude will rise as high as $135 a barrel for British oil.

"We believe that the market will continue to tighten to critical levels by 2012, pushing oil prices substantially higher to restrain demand," Goldman Sachs said in a research note.

A spike in the price of oil would also mean a big price increase for American crude.