A method of estimating the efficacy of an intervention on an oil or gas well based on allocating production for the oil or gas well in a lease comprising plural wells, wherein the intervention alters the state of the well and/or the well geometry, the method implemented in a computer system and comprising: receiving (101,216) at the computer system input data comprising measured well test data comprising data of how much fluid is produced by at least one well in the plural wells within a testing period collected at predetermined intervals during the life of the well, completion/recompletion data comprising data regarding events carried out to bring each well into production, and measured lease production data measuring how much fluid is cumulatively produced from the plural wells in the lease over time; detecting (101,212) with the computer system, through an outlier detection analysis, one or more outlying data points in the well test data; detecting (101,213) with the computer system, through a change point detection analysis of the well test data, one or more data points indicative of an intervention; generating with the computer system a decline curve (101,214,600) for each period in between the one or more data points indicative of an intervention and disregarding the one or more outlying data points; predicting with the computer system, using a machine learning algorithm, a decline curve for at least one well in the lease lacking well test data but having completion/recompletion data, wherein the machine learning algorithm is a regression algorithm to predict the decline curve based on at least the completion/recompletion data, wherein the algorithm is trained on a set of testing data derived from the input data to predict decline curves for those wells; determining with the computer system the estimated production of each of the plural wells in the lease for a predetermined period of time by integrating the decline curve for that well over the predetermined period of time; calculating with the computer system the allocated production for a particular well for the predetermined period of time in the plural wells by multiplying the ratio of the estimated production of the particular well to the sum of the estimated productions for all wells in the lease by a production per lease value for the period of time derived from the measured lease production data; predicting with the computer system future production amounts of the particular well based on the decline curve; and based on the predicted production, evaluating with the computer system the efficacy of an intervention on the particular well. receiving (101,216) at the computer system input data comprising measured well test data comprising data of how much fluid is produced by at least one well in the plural wells within a testing period collected at predetermined intervals during the life of the well, completion/recompletion data comprising data regarding events carried out to bring each well into production, and measured lease production data measuring how much fluid is cumulatively produced from the plural wells in the lease over time; detecting (101,212) with the computer system, through an outlier detection analysis, one or more outlying data points in the well test data; detecting (101,213) with the computer system, through a change point detection analysis of the well test data, one or more data points indicative of an intervention; generating with the computer system a decline curve (101,214,600) for each period in between the one or more data points indicative of an intervention and disregarding the one or more outlying data points; predicting with the computer system, using a machine learning algorithm, a decline curve for at least one well in the lease lacking well test data but having completion/recompletion data, wherein the machine learning algorithm is a regression algorithm to predict the decline curve based on at least the completion/recompletion data, wherein the algorithm is trained on a set of testing data derived from the input data to predict decline curves for those wells; determining with the computer system the estimated production of each of the plural wells in the lease for a predetermined period of time by integrating the decline curve for that well over the predetermined period of time; calculating with the computer system the allocated production for a particular well for the predetermined period of time in the plural wells by multiplying the ratio of the estimated production of the particular well to the sum of the estimated productions for all wells in the lease by a production per lease value for the period of time derived from the measured lease production data; predicting with the computer system future production amounts of the particular well based on the decline curve; and based on the predicted production, evaluating with the computer system the efficacy of an intervention on the particular well.