June 21 (Bloomberg) -- Petroleos Mexicanos, the state-owned oil monopoly, said crude production fell 6.6 percent in May from a year earlier and dropped to its lowest this year as the company struggles with declining output from its Cantarell field.

Daily output was 3.11 million barrels, down from 3.33 million in May 2006, the Mexico City-based company said today in a report on its Web site. January's production of 3.14 million barrels was the previous low for the year.

Cantarell, the world's third-largest oil field, produced 1.58 million barrels per day, a 15 percent decline from 1.86 million barrels daily in May last year. May's daily production at the offshore field was lower than 1.59 million barrels in April.

Pemex has increased its spending plan this year for exploration and production to 137 billion pesos ($12.7 billion) to increase production from other offshore fields, such as Ku- Maloob-Zaap, to make up for Cantarell's drop. Ghawar in Saudi Arabia is the world's largest oil field, followed by Burgan in Kuwait.

For the first five months of the year, Cantarell's output has dropped 17 percent from a year earlier to average daily production of 1.58 million barrels. Pemex had estimated a 15 percent drop at the field in 2007.

Pemex's crude production has fallen in the past two years after reaching a peak of 3.38 million barrels per day in 2004. Last year, the company produced 3.26 million barrels a day.

In May, Pemex received revenue of $3.03 billion on exports, lower than $3.22 billion a year ago and outpacing $2.74 billion in April. The company's average export price was $55.53 a barrel in May compared with $56.77 a year earlier. The average export price has climbed each month this year after sliding as low as $44.40 in January.

Natural gas production rose 12 percent to 5.94 billion cubic feet per day in May from 5.29 billion cubic feet daily a year earlier. Daily output fell from a record 5.97 billion cubic feet per day in April, the first drop from a previous month since October.

To contact the reporters on this story: Thomas Black in Monterrey at tblack@bloomberg.net

Last Updated: June 21, 2007 12:15 EDT