Mechanical and Electrical (M&E) services account for 10-70% of the total cost of projects, depending on the project type. Sadly, the complex nature of the design of M&E services among other peculiar attributes has led to an enormous challenge in the cost management of M&E services in the construction industry. This study examined the knowledge areas required to effectively cost-manage M&E services in construction projects. Data for the study were collected by administering copies of a carefully designed questionnaire among experts in M&E services after a pilot study with a team of experts. The variables outlined in the questionnaire were extracted from relevant literature. In selecting the M&E services experts that participated in the survey, purposive and snowballing sampling techniques were used. The professionals involved include electrical, mechanical engineers, and quantity surveyors. Data analysis was done using mean item score, gap analysis, Spearman rank correlation, and Kendall coefficient of concordance. Findings revealed that knowledge in Bill of Quantities (BOQ) preparation, valuation, measurement of M&E works, estimating, and quality management were ranked as the most important knowledge areas and a statistically significant agreement among the experts was recorded. Gap analysis revealed that the ability of cost managers/QSs in the knowledge areas is currently below expectation while a moderate relationship was observed between the importance and performance of QSs/cost managers in the knowledge areas. The study concludes that there is a need for cost managers/quantity surveyors to enhance their knowledge in the identified knowledge areas and strive hard to close the gap between importance and performance in the knowledge areas.