With gasoline prices over $4 a gallon in Maryland, some drivers of SUVs and pickups are paying more than $100 to fill up their tanks.

But if you think that's bad, head to a fuel dock, where higher prices and boats' bigger tanks mean fill-ups can cost thousands.

"I've got a 250-gallon fuel tank," said Ed Potter, a recreational boater from Edgewater. "Back when it was $1.92, I was crying about it. Now, it's insane."

Mr. Potter said it costs him more than $1,000 to fill up and he spends more than $600 on fuel for a day trip in his 37-footer.

"It makes me think twice before heading out," Mr. Potter said.

With gas...