That's interesting. Crude Oil (which is primarily what gasoline is made from) prices plunged from the around $80/barrel down to $72/barrel in early/mid December. They rallied fairly quickly and have been sitting around $80/barrel. I don't suspect that crude prices are behind the increase.
Quick increases in gas prices when crude prices aren't increasing are typically due to refining constraints. This can happen when there is a sharp decline in refining capacity (caused by a refinery accident or a refinery being taken offline for maintainance). I can also happen during the transition between blends. The US is divided into a patchwork of different gasoline blend regulations. If the refiners misjudge the demand for a blend, it can lead to shortages that drive up the price for a brief period in a region.