The invention relates to a method for producing products by microbial fermentation. The method comprises first converting a feed stream containing methane to a gaseous substrate comprising CO, of the invention include converting CO H2, and CO2 using a steam reforming zone and a water gas shift zone. The gaseous substrate is then converted to products such as alcohols and/or acids by to one or more products including alcohols and/or acids by fermentation using a carboxydotrophic microorganism.