Drivers of vehicles that run on natural gas have escaped prices above $4 per gallon for gasoline, but they're having to wait longer, or search harder, to fuel up along the Wasatch Front.

Many drivers of natural-gas vehicles say they have gone to filling stations in recent weeks only to find that increased demand has created insufficient pressure in the station's tank to pump the fuel. Those motorists have been forced to drive around searching for fuel, or they've had to come back to a station later to try again. Some have been forced to leave the station with less than a full tank.

Brady Knight of Lehi and two friends were filling up Monday at a Questar Gas fueling station in Salt Lake City. They were frustrated, however, by the lack of working pumps due to low pressure or no pressure at all. Only two of eight pumps were functioning properly. He was able to pump 7.52 gallons of compressed natural gas, at a total cost of $6.46.

"We've spent the last hour trying to find a natural-gas station," Knight said.

Other drivers of natural-gas vehicles also recently have found plastic bags over the fuel pumps.

Stephen Adams, who drives a 12-passenger natural-gas vehicle for his LDS Church ward, tried to fill up the van last Tuesday night, but he gave up after trying a local Tesoro station and a Questar Gas fueling station.

He was successful at 6 a.m. last Wednesday morning. But later that evening, when he wanted to top off the tank, he could not find a working pump.

"Our ward has a van that was donated, and we used the van to take people to the doctor or to groceries, different things like that," Adams said.

Adams also worries about the increasing price of natural gas, which he said recently went up 22 cents a gallon.

"I'm concerned that a lot of people who are trying to make the conversion — and it costs about $2,500 to do that — and they don't have an alternative if they don't leave a regular gas tank on," he said. "It's going to make it harder for all of us, the extra pressure on supply, if they're not going to be able to meet that."

Questar Gas Co. spokesman Chad Jones said the lack of pressure is a direct result of numerous drivers filling up one after another, which doesn't allow the pressure in the storage tanks to sufficiently recover.

He described the tanks as working like large balloons that lose pressure when fuel is pumped out. In order for the "balloon" to operate efficiently, adequate time is needed for the compressor to refill the pressure in the tank. When demand is high, there isn't always enough time, he said.

The problem could be alleviated somewhat if technology improvements were made to the natural-gas delivery system, said Questar analyst Darren Shepherd. However, he said, those upgrades would be costly and would require significant investment from private natural-gas fuel providers.