The fishingeffort of the Mexican tuna purse-seine fleet for the period 1984-1986 wasstandardized using a principal component analysis of the following vesselcharacteristics: age built, gross and net tonnage, overall length, breadth anddepth of the vessel, carrying capacity, horsepower and area of the net. Thethree first principal components explained 85% of the total variability;however, only the first one is needed to calculate the fishing power of an individualvessel. This method has two principal advantages: it avoids reliance on asingle character, and it makes possible the calculation of continuous valuesfor fishing power.