The study was on Comparative Assessment of Compliance of Oil Producing/Base Logistics Companies’ EMS with ISO 14001 Standards in Rivers State, Nigeria. The study made use of a cross-sectional research design. Companies were made to participate through convenience sampling of companies in the sampling frame. Being survey research, the instruments were administered on every willing respondent found in the HSE department of the companies surveyed. Out of 125 respondents, only 120 participated. Data collected were analyzed using percentage rating and simple descriptive statistics. A criterion means value of 2.5 was used as a benchmark for checking compliance and other assessment indices. This was drawn from the Likert scale of 4, 3, 2, and 1. In checking compliance, for instance, out of the 5 items considered, Total E&P Nig. Ltd attained the 2.5 mark in 4 items whereas INTELS Nig. Ltd hit 3 of them. Moreover, the two companies are compliant in most of the components as they rated 2.5 in the compliance rating matrix with Total E&P Nig. Ltd taking the lead. The study came up with some recommendations: The government of Rivers State should ensure that all oil and gas companies especially the Oil-producing and Base Logistics companies in Rivers state run their businesses in tandem with the concept of sustainability by first encouraging them to adopt ISO 14001 standard.