they must have non fastidious nutrient requirements since laboratory culture media would be prohibitively expensive for field application where huge volumes are injected the cells must be able to grow and produce the desired product under in situ conditions of ph temperature heavy metal ion concentration etc although some oil bearing formations are too hot impermeable or otherwise inhospitable to microbial presence many are within a temperature range of 20 u00b0 80 u00b0 c and can support microbial presence and growth microbes used for meor must also be non pathogenic and must not produce any animal or plant toxins since they may be injected near water supply aquifiers although many microbes can utilize hydrocarbons as the sole carbon and energy source all known species that do this are aerobes which require molecular oxygen for the initial attack on hydrocarbons if facultative anaerobes are used for meor non petroleum carbon sources should be supplied unless hydrocarbon utilizing anaerobes can be created through recombinant dna techniques sufficient non hydrocarbon metabolizable components must be present in the petroleum suitable carbon substrates are cheap carbohydrates such as molasses and whey and possibly inexpensive synthetic substrates such as methanol nitrogen phosphorous and other nutrients must also be supplied if these are not present in the carbon substrate or in the rock nutrients must be supplied at the correct time that microbial activity is desired loss or absorption of nutrients would be an economic debit facultative anaerobic halophilic or halotolerant thermotolerant bacteria may be used to achieve profile modification through the production of exopolymer and or the growth of cells within highly permeable rock thereby decreasing the permeability of this rock the exopolymer forms an insoluble matrix within the rock pores which is resistant to bio shear and thermal degradation ionic or other.