In SPE 89325, summarized in the March 2005 issue of JPT, Barree and Conway state that “new experimental data, under high-rate flow conditions, showed conclusively that Forchheimer’s equation, like Darcy’s law, has a limited range of applicability.” We agree with Barree and Conway that when flow tests have significant non-Darcy effects, interpretation is not always straightforward. However, we disagree with Barree and Conway that Forchheimer’s equation cannot be used to describe pressure-loss velocity dependency at high rates of practical relevance, and we would like to present data collected in two other laboratories to support our point of view. At FracTech, high-rate gas-flow tests on proppant packs have been conducted since the early 1990s. The tests are typically conducted with nitrogen at ambient conditions to measure the flow rates accurately. Fig. D-1 shows a Forchheimer graph for 20/40-mesh sand at 2-lbm/ft2 concentration for values of ρv/µ up to 330. The data show a linear trend with a coefficient-of-determination value, R2, of 0.9991. This range for ρv/µ is double that in Fig. 2 of SPE 89325. These data were originally presented in SPE 90406. Fig. D-2 is another Forchheimer graph from SPE 90406. The data presented are for resin-coated lightweight proppant with a 16/20-mesh size distribution. Again, a linear relation with an R2 of 0.9998 is observed over the range of ρv/µ values from 10 to 320. At Halliburton’s European Research Center (ERC), high-rate flow tests on proppant packs have been conducted with water as the flowing medium. Fig. D-3 shows the results of two such flow tests with 18/30-mesh high-strength proppant at 160°C and 10,000-psi stress. Again, the Forchheimer graphs show a linear trend (R2 of 0.99+) for each test over a similar range of ρv/µ values for which Barree and Conway claim nonlinear behavior. Last, but not least, we would like to share a Forchheimer graph for a pack of 1-in.-long pins as shown in Fig. D-4. The Forchheimer plot, shown in Fig. D-5, again shows a linear behavior over the entire ρv/µ range evaluated. The shape of the particulate used appears not to affect the linear behavior. The main difficulty in the use of the Forchheimer graph is illustrated by the two data sets presented in Fig. D-3: Although the slope of the lines is almost identical (meaning identical Beta factors), the intercepts with the y-axis that represent the inverse absolute permeability differ significantly. We conclude that, for practical purposes when non-Darcy effects are important, the Forchheimer equation and graph can be used.