The correct answer is option 4 - Indonesia. OPEC (Organization of the Petroleum Exporting Countries) is an intergovernmental organization founded in 1960 by five oil-producing countries, including Iran, Iraq, Kuwait, Saudi Arabia, and Venezuela. OPEC`s main objective is to coordinate and unify the petroleum policies of its member countries and ensure the stabilization of oil markets. Over the years, several other countries have joined OPEC, including Indonesia.

Option 1 - Vietnam is not a member of OPEC. Vietnam is not a major oil-producing country and therefore does not have membership in OPEC.

Option 2 - Philippines is also not a member of OPEC. The Philippines does not have significant oil reserves and is not involved in the production or export of petroleum.

Option 3 - Laos is not a member of OPEC. Laos is a landlocked country in Southeast Asia and does not have significant oil reserves or a role in the global oil market.

In summary, the correct answer is option 4 - Indonesia, as it is a member of OPEC.