This research work is on the accounting system standards involved, accounts kept and the effectiveness of the internal control system in operation in Nigeria oil companies using the Nigeria National petroleum corporation (N.N.P.C) as a case study. In conducting the study, the researcher has employed personal interview and observation as basic techniques of investigation. The findings reveals that the NNPC’s accounting system produce enough information through internal financial documents needed in the ordinal y course of operation but major accounts for publication purposes are not produce. It is system of internal control met common standards and effectively served its needs. In preparing its account, the NNPC however need to work at eliminating the problems largely arising from the intricacies sand complexities of operations in the oil industry. This can only be achieved with less government interference, institutions of additional disclosure requirement particularly in recognition of leadership and monitoring role of the NNPC in the industry. The researcher also found out that these are crying need for adherence to standard that can create uniformity of the accounting system in the oil industry.