Measurement of the filtration or water loss and wall cake building characteristics are basic to drilling fluid control and treatment. The filtrate collected is a measure of the relative amount of fluid in the drilling mud lost to permeable formations. Fluid loss values of 10 to 20 mL per 30 minutes are sufficient in most situations. Chemical studies of the filtrate are necessary in any successful mud control program. Analysis of the filter cake deposited in terms of thick-ness, composition, and consistency are also important considera-tions. These characteristics are controlled by the type and quanti-ties of solids in the fluid and their physical and chemical interac-tions. Different temperatures and pressures can have a big effect on filtration control. Therefore, tests are run at both low-pressure / low-temperatures and high-pressure / high-temperatures. The OFITE low-pressure filter press design features a cell body to hold the mud sample, a pressure inlet, and a base cap with screen and filter paper. Suitable for field and laboratory use, these units have become the industry standard for low-pressure / low-temper-ature filtration testing. OFITE also manufactures other types of filter press units and inventories a full line of replacement and consumable parts. Stainless steel cases are available for most of the units. When sev-eral tests must be run simultaneously, as in a laboratory environ-ment, multi-units are available in either two, four, or six-cell designs. These multi-units come complete with manifolds and all necessary air hoses and bleed-off valves. The field portable units are supplied with various pressurization assemblies and manifolds and rely mainly on carbon dioxide bulbs and nitrogen gas to pro-vide pressure. The American Petroleum Institute (API) recom-mends a standard 100 ± 1.0 PSI (690 ± 6.9 kPa) cell pressure be applied within 30 seconds for a 30 minute test.