In the petroleum and allied industries, there has been an increasing demand for reliable viable counts on fuel samples, and a membrane filtration procedure, IP385/95, and an emulsification procedure AFNOR MO7070/92, have been standardised. The former is unsuitable for on site use, and although the latter can be coupled to a Dip-slide test, it inherits the limitations of this procedure. The methodology described was a direct response to the need for a sensitive, quantitative on-site microbiological test for fuel, but the technology can be applied to any aqueous and non-aqueous sample. A nutritive solution, which may, if required, be selective, is gelled with thixotropic and/or pseudo-plastic agents instead of agar. A sample can be dispersed in the gel by shaking, and the gel is allowed to re-set as a flat horizontal layer. During incubation, colonies develop comparable to colony formation in ‘shake’ plates. In the preferred configuration for fuel-testing, ca. 16 ml of gel is dispensed into screw-capped rectangular glass containers ca. 65 ml capacity. During incubation, a sensitive redox indicator gives an early indication of colony growth. The accuracy is similar to a shake plate. Very large numbers of microbes produce a coloured formazan within a few hours—a real time test. The gel composition described has been formulated so that non-aqueous samples emulsify and completely disperse. The formulation has been used to test diesel fuel and aviation kerosene; the results are comparable to the methods IP385/95 and AFNOR M07070/92. Preliminary results of tests on water, milk, emulsions, etc. suggest that the methodology will have wide applications in the laboratory but particularly on-site.