The effort of developing this new method to measure naphthenic acid corrosion potential has been further pursued in this paper. The iron (Fe) powder testing procedure has been modified and a new iron powder supplier was used. Several crude oil samples were tested and classified accordingly. To be able to compare with previous results, some crude oil samples were tested again and a corrective factor was introduced. This is because the superficial area of the previous Fe powder used was ten times larger than the one currently in use. The classification thus achieved still maintained the same previous trend in that it does not necessarily keep equivalence with the total acid number (TAN or neutralization number). That is, crude oils having lower neutralization number appeared more corrosive than other having much larger TAN. The objective here was to develop a more reliable testing method than those currently available, capable of being used as a predicting tool for corrosivity in the plants. Keywords: Naphthenic acid corrosion, crude oil corrosiveness, corrosivity tests, total acid number, iron powder test.