Columbia subject headings:
Mexico--Economic conditions--1918-
Mexico--Social conditions.
Petroleum industry and trade--Mexico.
Petroleum industry and trade--Venezuela.
Petroleum law and legislation--Mexico.
Petroleum law and legislation--Venezuela.
Venezuela--Economic conditions--1958-
Venezuela--Social conditions--1958-1999.
Harvard subject headings:
Mexico--Economic conditions--1918-
Mexico--Social conditions.
Petroleum industry and trade--Mexico
Petroleum industry and trade--Venezuela
Venezuela--Economic conditions--1958-
Venezuela--Social conditions--1958-
Princeton subject headings:
Petroleum industry and trade--Mexico.
Petroleum industry and trade--Venezuela.
Petroleum law and legislation--Mexico.
Petroleum law and legislation--Venezuela.