The study traces the evolution of West African economic integration efforts, leading up to the formation of the Economic Community of West African States (ECOWAS). The original Lagos Treaty of 1975 is reviewed against the background of its revised 1993 Abuja version under the framework of the Customs Unions theory. This study is undertaken to ascertain the consistency of regional integration theory with the stated objectives of ECOWAS. It questions, for example, whether the Customs Unions theory and its welfare effects could actually explain the experience of regional integration of West Africa in general, and within ECOWAS in particular. In other words, the critical success factors and/or moderating influences in ECOWAS are examined against the background of the Community's objectives as set out in its two Treaties. The study also benefits from a wide range of discussions on different political and economic bases for regional integration theory: functionalism, neofunctionalism, federalism and intergovernmentalism and their relevance to ECOWAS. Strange enough, while these 'isms' are demonstrated to be inconsistent with ECOWAS objectives having dwelt more on regional integration efforts in Europe, no other study on West African integration has examined ECOWAS along these lines. The experience of ECOWAS is made against the backdrop of Customs Unions within Africa, such as the Arab Maghreb Union (AMU), East African Community (EAC) and the Southern African Development Community (SADCC); and others outside Africa in regions like the European Union (EU), North American Free Trade Area (NAFTA) and the South American Customs Union (MERCOSUR). One emerging pattern of such comparison reveals that ECOWAS has wavered from its stated objectives in favour of the static principles of customs unions theory and consequently been unable to improve its record on the welfare levels of contracting states. The implication of such departures from its original objectives is that market inter-penetration and intra-regional trade within ECOWAS has neither yielded the desired welfare gains nor improved levels of industrialisation, sustained growth and economic development. It is safe to conclude, therefore, that despite considerable efforts at achieving regional economic integration in ECOWAS, the result has been dismal largely as a result of applying unrealistic models of customs unions theory to the West African situation. It is therefore posited that the process of regional economic integration in other parts of the world and particularly in Europe, are not readily applicable in the West African context, where the economic, political and institutional foundations are not only grossly dissimilar but largely at variance.