Modularization procedures result in substantial cost savings in mega Oil & Gas projects. Little industrial guidelines are available in North American and European codes of practice for effective modular constructions. Attempts were made over the past few years by EPCM companies to develop design rules to improve modularization strategies and meet the aggressive industrial demands. Unfortunately, absence of industrial rules has generated randomness in the design procedure with no technical justifications. The paper offers cost effective strategies and industrial guidelines that can be used by practicing engineers and steel fabricators for modular steel designs for Oil & Gas projects. Structural, piping, mechanical and electrical engineering guidelines are briefly discussed. Several examples are provided for various process & building facilities to illustrate the efficiency of these modularization strategies. The described procedures and recommendations can be used in practice to maximize the project savings in the Oil & Gas industry.