Objective: Phosphate-bonded investments are being investigated for use as die materials for dental superplastic forming. The effects of handling technique on the strengths of these investments needs to be determined. The purpose was to use methods of Weibull analysis to fit measured 4 point bend strength data and determine strength and Weibull modulus, where modulus represents the scatter of the data. Materials and methods: Weibull parameters were determined using methods of regression and maximum likelihood using 2 and 3 parameters. The parameters were x(0) the lower bound of strength, m the Weibull Modulus, and theta the characteristic strength. x(0) is zero for the 2 parameter models. In addition to plots of the measured data and curves generated using the Weibull parameters, the fit of the models to the measured data was determined using correlation coefficient and the chi (2) statistic. Results: The results showed that characteristic strength was similar whether determined using regression or maximum likelihood, 2 parameter or 3 parameter models. However, Weibull Modulus was significantly lower for 3 parameter models than for 2 parameter models. Visually the 3 parameter models give the best fit for the majority the data sets. Correlation coefficient, r, showed whether the method of maximum likelihood or the method of regression was more appropriate. chi (2) and correlation coefficient did not necessarily give the same indication of goodness-of-fit of these data sets. Significance: Strengths of dental phosphate-bonded investment materials can be described well using weibull analysis which gives characteristic strengths and quantitative measures of scatter of the data in the form of Weibull Modulus. These may then be used to select a handling technique to produce dies for dental superplastic forming.