This paper presents a detailed formulation of a rate of penetration (ROP) model, consideringmany drilling parameters and conditions for obtaining maximum drilling rate as well asminimizing the drilling cost.A regression analysis technique has been usedfor ROP modeling in Mishref formation.The datawere extracted from routinely available mud and wirelinelogs. These data includes weight onbit ,rotary speed,horse per square inch,and transit time.For ROP modeling, data of five wellsinHalfaya oil field in south Iraq were extracted.Statistical software called SPSS was used forimproving the modeling data and to perform linear and nonlinear multiple regression analysis.This improving approach included detection the outliers of modeling parameters, grouping themodeling data, moving average and finally applying the regression analysis.Results of modeling showed that the grouping of modeling data exhibited good convergencewith actual data and the overall model of oil field could produce good fitness with the actualdata in both cases of linear and nonlinear models.Also,a good estimation of drilling cost couldbe obtained when using this model.