Gasoline prices have increased by more than 30 cents per gallon since February, according to WEX’s March fuel prices report. The national average is now $3.57 per gallon, its highest level since early September, but still nearly 8 cents per gallon lower than last year.

Unfortunately for fleet managers, most analysts are predicting that prices will continue to head higher over the next 30 days, with some forecasters calling for a peak above $3.75, says WEX.

Market-watchers point to the summer fuel switchover as the primary cause, which is mandated by the EPA and is more expensive to make. Not only are increased costs a factor, but speculators also fear that supplies will be too tight to meet the increased summer drive season.

The good news is that most experts don’t believe the increases this year will be as great as in past years. Consumption of fuel is down and crude costs — especially domestic crude — is comparatively low, says WEX.

However, they do caution that hot spots could break out in response to regional disruptions, which are caused by low ethanol supplies (ethanol makes up 10% of the gasoline formula in most areas) or a refinery issue.

Meanwhile, diesel prices have been hovering around the $4 per gallon mark, says WEX. With the end of heating oil season on the horizon, analysts predict that prices of diesel will ease in the coming weeks.