ET today, oil major ExxonMobil (NYSE: XOM) is down 2.2%, while downstream from Exxon, refiner Phillips 66 (NYSE: PSX) is seeing its shares slide 3.3%. There's no obvious, headline-grabbing explanation for the relapse -- rather, just generalized concerns about the prospect of economic weakness in China and a potential recession here in the U.S., making investors wonder if demand for oil is about to take a hit. With gasoline prices retreating from highs near $5, and toward the $4.50 range instead, motorists are nevertheless still upset that gas costs more than twice what it did a couple years ago.