The study investigated related party transactions and firm's financial performance using Secondary data obtained from Nigeria stock Exchange. We tried to determine whether RPT is used by firms to manipulate and bloat Return on Asset, Return on Equity and Earnings per share of manufacturing firms. RPT was subjected to Hausmann test for selection of appropriate model and regressed against performance variables. Test of causality was conducted to determine whether causal relationship exist amongst variables of study. Result showed RPT has no significant effects on ROA and EPS and not used to manipulate ROA and EPS. Conversely, RPT has significant relationship with ROE without any causal relationship which may be attributable to the shareholding structure of the firms. The study confirmed positive relationship of RPT with ROA, ROE and EPS implying that increases in RPT increases performance and in contrast decreases in RPT decreases performance. Based on findings, we concluded

The debate over choice of Accounting methods in the oil and gas sector in the face of alternatives between Full Cost and Successful Effort method dates back to the mid 2oth century and is unlikely to abate soon. Full cost method capitalizes all costs while Successful Efforts method capitalizes only cost that discovers reserves and expenses 'dry hole' costs. The debate is further fueled by the inability of regulators to choose one method over the other leaving the decision to the whims and caprices of the firm who may choose one method over the other to mask their real intentions. This paper examines the pros and cons of the two methods. Investors must be weary and realize that any of the methods adopted represents a historical perspective that is not reflective of the economic reality especially reserves under successful Effort method. Investors must note that using Full cost method approximates the book values of the reserves close to the economic value while at the same time it suffers from the disadvantage that it can be used to mask unprofitable investments. In summary, the raging arguments reveal the possibility of manipulation of earnings by oil firms depending on intentions through choice of accounting method. In Nigeria, Multinational firms tend to adopt accounting method in line with the method chosen by the parent company to ensure uniformity and ease of comparison of results while indigenous firms adopt the methods that best suit their operations

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