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The values of parameters measured or interpreted are often not provided at the correct level of accuracy. It could result in unnecessary waste of time in report preparation, presentation and negotiation. This paper discusses and recommends the reporting accuracy of parameters that are frequently used in the upstream petroleum industry giving due consideration to the errors during the measurement and interpretation process before assigning a value to a parameter. Every parameter could be identified as a first level report (direct or indirect measurement), second level report (calculated from a direct or indirect measurement), third level report (calculation involves using second level reports) or fourth level report (determined by analogy or calculated from an empirical equation using at least one second level report). Reporting accuracy can be guided by the uncertainty or percent error in a parameter and hence the applicable number of significant digits (sd). A significant digit is defined as any digit that is necessary to define the specific value or quantity. The number of significant digits of a numerical value is the number of digits except for zeroes at the beginning and at the end. Zeros may be used either to indicate a specific value as does any other digit, or to indicate the magnitude of a number. Uncertainty in parameters that represent a spatial estimate generally reduces from the exploration to development to production phase. Hence, Reserves could be presented in 3 sd but Prospective Resources should be presented in only 2 sd. Contingent Resources can be reported in 2 or 3 sd. This paper will also summarize the recommended reporting accuracy for parameters commonly used in conventional and unconventional resource * MB Energy estimation, in tabulated form making this paper a useful reference document for all professionals involved in the technical or commercial aspects of the upstream petroleum industry.