Mexican state oil monopoly Petroleos Mexicanos (search) on Monday announced it had recovered about two-thirds of the estimated 5,000-barrels of oil that spilled last week into a river feeding the Gulf of Mexico (search).

But at least 55 percent of oil-soaked matter along the Coatzacoalcos River and southern Gulf of Mexico in Veracruz state remain to be collected, according to a news release from Petroleos Mexicanos, or Pemex.

Contacted Monday evening, representatives of Mexico's Environment Department (search) had not seen the cleanup report by Pemex and could not immediately verify its contents.

The spill occurred after an explosion Wednesday at a pumping station near Santiago Tuxtla, about 250 miles east-southeast of Mexico City. The blast caused a burst of high pressure that ruptured the oil line 70 miles (110 kms) away in Nanchital, just south of the Gulf port city of Coatzacoalcos.

Four of the five people injured in the explosion remained hospitalized Monday in Mexico City and Coatzacoalcos, with one man in grave condition.

Flowing into the Gulf of Mexico, the oil spill initially spread across 5 miles (8 kms) on coastline, restrained somewhat by contention booms.

By Monday morning, beaches straddling the mouth of the polluted Coatzacoalcos River had been completely cleared of oil, Pemex said.

The state oil company estimated it had collected 4,950 cubic meters (175,000 cubic feet) of solid material contaminated by oil — about 45 percent of the 11,000 cubic meters (390,000 cubic feet) soaked by the spill.

The Environment Department has said it could file a criminal complaint against Pemex and fine it as much as US$200,000 (euro148,000) for the spill.

Reporting on the public-health effects of the spill, Pemex said its medical services have treated 24 people at a company hospital in Nanchital and 59 patients in house calls after receiving reports of migraine headaches and irritation of the mouth, nose and throat.

About 300 people continue to work in the cleanup effort.