Ryder Scott designed the Lognormal Probability Tool to assist the experienced petroleum professional in developing assessments of undeveloped reserves and resources quantities in resource plays. The tool is based on the methodology outlined in Monograph 3, “Guidelines for the Practical Evaluation of Undeveloped Reserves in Resource Plays (2010),” published by the Society of Petroleum Evaluation Engineers. The template displays a probit plot with up to three lognormal distributions, each containing as many as 4,000 data points. The Lognormal Probability Tool features utilities for sorting data series. It also offers options to select the data interval over which the linear regression will be conducted (if desired), and adjustment ranges for the logarithmic scale of the probit plot. With the preparation of the probit plot itself, the program will also determine and display the results of the analysis to include P10, P50 and P90 distributions; lognormal series mean; arithmetic mean; and Swanson’s mean. Also provided are Monograph 3 metrics P10/P90 and p̂. Finally, the tabulation will display the count of data points included in the linear regression and indicate the conformance of the analysis to the criterion presented in Monograph 3, namely, whether the analyzed sample size meets the minimum recommended size.