The price of regular gasoline broke $4 in Whatcom County, and prices at stations around Bellingham were pushing closer to that amount Tuesday.

Meanwhile, an increase in the wholesale cost of gasoline could drive prices at the pump even higher, said Tim Hamilton, executive director of Automotive United Trades Organization, which represents gasoline retailers.

“Is this the top end? No. More to come,” he said.

Gas station owners are feeling the profit margin pinch because of higher wholesale prices and fixed percentage fees taken by credit card companies, he said.

Hill’s Chevron in Blaine on Tuesday charged $4.09 a gallon for regular gas. With gasoline priced more than $1 a gallon higher in British Columbia, the station is still getting a lot of customers crossing the border to buy, station owner Mike Hill said.

“They’re saving more than they’ve ever saved,” he said.

In Bellingham, the price pushed close to $4 a gallon at some stations. The Bellingham Shell at the corner of Kellogg Road and Meridian Street was selling regular unleaded for $3.99 a gallon.

Diesel prices set another record Tuesday, reaching $4.55 a gallon in the Bellingham area, according to the AAA Daily Fuel Gauge Report.

Janet Ray, spokeswoman for AAA Washington, said it’s hard to know what summer prices will look like until the number of drivers on the road during Memorial Day weekend can be gauged.

People are buying less gas, but investors speculating on the future values of oil are still driving up oil costs, she said.