Environmental awareness is growing globally largely due to the increased frequency and severity of natural disasters. Carbon dioxide emissions in the transportation sector are among the highest of all sectors contributing to global warming. As such, there is growing interest in finding green alternatives to fossil fuel use. This study explores methods of producing heterogeneous acid catalysts used in the production of biodiesel, a fuel that serves as an alternative to conventional diesel. Different biomass sources were used to create carbon-based catalysts called biochar, which have the potential to be not only sustainable, but also more environmentally friendly when used in the esterification of oils for the production of biodiesel. These catalysts were created from sucrose, banana peel, corn starch and corn starch with added iron nitrate. The catalysts were synthesized using two different methods: the first method, carried out in two stages, partially carbonizes the biomass in the first stage and in the second stage sulphonates it with sulphuric acid to give the charcoal its catalytic capacity. The second method performs these two stages in a single step where the sulphonation is done together with the carbonization. These catalysts were tested in laboratory trials in the esterification of oleic acid with methanol in two different oil-to-methanol molar ratios of 1:5 and 1:10. Samples were taken at fixed time intervals to be analysed by Fourier-transform infrared spectroscopy to determine the yield rate of methyl oleate. The catalyst used was also analysed by the same method to identify the functional groups present on the surface of the catalyst. Of all the catalysts tested, the one with the highest yield of methyl oleate was the banana peel catalyst, with an average yield of 92.3% at a molar ratio of oil-to-methanol of 1:10. The second best yield rate was obtained with the starch and iron nitrate catalyst synthesized with 80g of sulphuric acid, which obtained a rate of 58.2% at the same oil- to-methanol molar ratio of 1:10. The catalysts had similar functional groups, with a predominance of sulphonic acid and carboxylic acid groups. The biofuels industry is interested in investing in alternatives for biodiesel catalysis, especially if the catalysts come from waste that can be obtained sustainably. Eventually fossil fuels will be replaced by cleaner, more sustainable and environmentally friendly energy sources, and it is therefore important to carry out studies that promote new technologies and methods in this sector to make this goal a reality.