One in every seven Texas gas stations is without fuel a week after the historic freeze crippled refineries and trucking, and the second-largest U.S. state may need to seek outside help.

The number of filling stations and convenience stores with empty tanks reached 15% across the Lone Star state as of Wednesday morning, according to the Texas Food & Fuel Association and retail tracker GasBuddy. Shortages are most acute in Lubbock, El Paso and Odessa in West Texas, GasBuddy analyst Patrick DeHaan said in email.

After last week’s historic freeze crippled some of the continent’s largest oil refineries, diesel shortages and impassable roads halted or delayed fuel deliveries to many stations. A large tanker can haul about 10,000 gallons of fuel—enough to fill 400 pickup trucks.

The Texas Food & Fuel Association urged motorists to show restraint and avoid “panic buying.”

“We would ask our fellow Texas not to engage in panic buying and be patient with us,” said Paul Hardin, the association’s president. “We missed four days of the trucks getting to stations as we kept our drivers safe and off the roads, and we are in catch-up mode now.”

The supply pinch was a contributing factor in Wednesday’s jump in gasoline futures to a 19-month intraday high of $1.90 a gallon on the New York Mercantile Exchange.

Hardin said adequate gasoline and diesel inventories are stowed in pipelines and at storage hubs for short-term needs once it can be delivered by truck. But if refinery outages drag on for a full month, Texans will be dependent on supplies from other states, he said.