Is expensive oil worth it?

As for its other fields, 40% of Mexico's remaining reserves are in the Chicontepec Field, which was found in 1926, but which has remained undeveloped because the oil is trapped in impermeable rock. The remainder of Mexico's fields are much smaller, much more expensive to develop, and contain heavy oil that buyers do not want. As a result of concentrating on its one good oil field and ignoring everything else, Mexico's proven reserves have fallen every year for more than a decade, and it has less than 10 years worth of oil reserves at current production levels.