Oil may have biggest monthly gain since 1999

Oil prices really moved up last year and at one point hit $147 a barrel. That has to be the fastest ascent in oil prices in history, right? Wrong -- at least not on a monthly basis. Oil's May increase will be the sharpest monthly increase since 1999.

Many analysts can't come up with a good set of reasons for crude prices to rise. The economy is still sluggish in most major world economies, excluding India and China. Production rates are steady and OPEC said it will not change output quotas. There may even be an oil surplus in the U.S.