(Repeats story from Sunday to additional subscribers)
May 18 (Reuters) - Mexico's Pemex has quietly begun shipping light Isthmus crude to a variety of West Coast refiners this year, according to U.S. and Reuters data, resuming such sales after a six-year hiatus.
The state-run oil company, which exported only about 100,000 barrels per day (bpd) of Isthmus last year, shipped about 340,000 barrels of the crude to Valero Energy Corp at Benicia, California, in January and February, according to U.S. government data.
It sent another 350,000 barrels (48,000 tonnes) to Tesoro Corp in San Francisco in March, according to Eikon's trade flow database based on PIERS data. Pemex then exported another 150,000 barrels to Shell Trading at Anacortes, Washington, in May from the Salina Cruz terminal.
Isthmus is typically shipped to Gulf Coast and East Coast ports including Beaumont and Corpus Christi, Texas and Philadelphia, Pennsylvania.
The move is the latest in a series of new export contracts that Pemex has announced, aimed at diversifying the company's base of clients. Pemex said it began shipping Olmeca crude to Europe in January, and last month said it started shipments of Isthmus to Hawaii.
A sweeping energy overhaul in Mexico passed late last year and pushed by President Enrique Peña Nieto seeks to inject competition into a sector dominated for decades by Pemex and to boost domestic crude output, which has fallen by a quarter since 2004 to about 2.5 million bpd.
Over the same period, the country's oil export volumes have dropped by a third.
The light, sweet grade of Isthmus crude oil with 33.6 API degrees is mainly produced in the southern Gulf of Mexico's Campeche zone with a principal loading port at Pajaritos.
Pemex had halted exports of Maya crude to the U.S. West Coast in 2008.
The Mexican oil giant exported a total of 1.2 million bpd of crude oil last year.
Pemex normally supplies Exxon Mobil Corp one monthly cargo of 500,000 barrels in Houston. Pemex also delivers Total Petrochemicals at Port Arthur, Texas, 150,000 barrels of Isthmus monthly.
Citgo Petroleum, PBF Holding, Atlantic Trading, Chevron and Shell also buy varying sized cargoes of Isthmus occasionally. (Reporting by David Alire Garcia in Mexico and Marianna Parraga in Houston; editing by Jessica Resnick-Ault and G Crosse)