A methodology for horizontal well test interpretation in both compressible and bounded or infinite unconsolidated reservoirs with a single fluid is presented. Algebraic expressions are developed from characteristic points and lines found on the log–log plot the pressure and pressure derivative versus time log–log plot, to determine horizontal permeability, well-drainage area and permeability modulus were developed for the two external boundary condition cases dealt with. The results obtained from the developed equations provided good results as they are demonstrated by the application to synthetic examples.