The fabulous early history of the Mexican oil industry, the Tampico embayment, the Golden Lane, the huge gushers, and the emergence of Petroleos Mexicanos as the dominant factor in the Mexican petroleum industry are known to most persons in the oil and gas industry. Not so well known, however, is that Mexico has large reserves and is an important producer of natural gas, some of which is exported to the United States. Moreover, the fine record of Petroleos Mexicanos in exploration and exploitation of Mexico's petroleum resources, and the rapid increase in reserves and in the use of natural gas as an energy source in Mexico as long-distance transmission lines are built to major markets, never have been appreciated outside of Mexico.

There are four petroliferous areas along the eastern Gulf Coast of Mexico, the western end of the Gulf Coast embayment. However, only two are of major importance as gas-producing regions--the northeastern area, the Burgos basin, which is the southward extension of the Rio Grande embayment of the United States, and the Isthmus-Tabasco region in southeastern Mexico. Although several small gas discoveries have been made in the Vera Cruz embayment, results of exploration there have been disappointing. The Tampico embayment, largest oil-producing region in Mexico, contains only one important source of natural gas, Poza Rica, where there is a huge reserve of associated and dissolved gas. However, the quantity of gas available is limited by the quantity of oil produced. Furthermore, much gas produced in Poza Rica is returned to the reservoir to increase oil recovery and will not be available for many years. Also, the gas contains an average of as much as 20 per cent carbon dioxide and much hydrogen sulfide, which must be removed to meet requirements for markets. The remainder of the natural gas in the Tampico embayment is in small quantities accompanying oil and contains large but varied amounts of acid gas, often toxic. It is used in field and plant operations and for pressure maintenance.

Most of the natural gas in the northeastern region, the Burgos basin, is nonassociated, although there is associated gas in a few fields. Gas is produced from Miocene, Oligocene, and Eocene sandstone. The Tertiary fields are on southward extensions of trends from those in the United States and are on closed structures. Recently, two discoveries have been made in Cretaceous carbonate rocks on the western side of the basin, but the importance of Cretaceous production remains to be demonstrated.

The second important gas-producing area in Mexico is the Macuspana basin in the Isthmus-Tabasco region, which contains the huge Jose Colomo field, the largest single gas reserve in Mexico. Most of the fields in the basin produce nonassociated gas. There is associated and dissolved gas in many fields, particularly in the Isthmus Saline basin adjoining the Macuspana basin on the west. Many fields in the Isthmus Saline basin are on salt diapirs.

Natural gas from the Burgos basin is transmitted to the northern Mexico industrial area, although some is exported to the United States. Natural gas from the Isthmus-Tabasco region and some from Poza Rica in the Tampico embayment is transmitted to the Mexico City industrial area. Gas is processed in four huge absorption plants near the sources before transmission to market. Large quantities of natural gas liquids are removed. Although demand for natural gas is increasing rapidly, many large favorable areas are explored only partially or are unexplored.