Gas prices in the state of California have risen to the point where it’s now cheaper to fill up in Mexico.

In the last five days, gas has increased US 53.7 cents in the coastal border city of San Diego, with the average price now over $4 per gallon due to supply shortages. In Tijuana, however, 24 kilometers south, gas prices remain unchanged at 13.57 pesos per liter, equivalent to US $3.27 per gallon.

The trend started late last week when gas prices in San Diego became more expensive than in Baja California. Self-serve regular gasoline in San Diego increased 15.2 cents on Sunday after having increased 16.7 cents on Saturday and 8.4 cents on Friday.

The increases continued into this week: on Monday in San Diego the average gallon of regular reached $3.50 and has continued to rise. Some observers believe gas prices could continue going up before settling in the fall.

Marie Montgomery of the Automobile Club of Southern California cited inadequate supply. She said Southern California refiners were outbid by Mexico competitors for foreign oil last week, and therefore failed to receive any new shipments.

Plus the ExxonMobil refinery in Torrance, California, is still offline as the operator awaits permission from the South Coast Air Quality Management District to use refurbished equipment during repairs, Montgomery added.

In the 1970s, as inflation and supply shortages forced rationing in the U.S., Baja California prices were 50% of those north of the border. Diesel in Baja California during that time cost 25 cents.

“I remember I had a VW Rabbit diesel, into which I installed an extra 10-gallon tank,” author and chef Udo Winkler told Mexico News Daily. “And I used to think that it was cheaper to see customers in my diesel than it was to make a phone call. The drive from Redlands [California] was about 1-½ hours to the border. Got some tacos for lunch and headed back. The diesel at that time got 44 miles per gallon, and at .25 cents per gallon, the trip was well worthwhile.”

Sources: Daily Bulletin