Precipitation of calcium naphthenate soaps from acidic crude oils poses significant operational challenges. Calcium naphthenate deposition in oil fields results from the interaction of a family of special polycyclic tetracarboxylic acids, known as ARN acids, with divalent metal ions (Ca2+) present in produced water. Calcium naphthenate scaling is being increasingly reported from oil fields in South America. We report detailed analyses of three field deposits from various crude-oil-producing fields in South America. All the field deposits were confirmed as calcium naphthenate scale via advanced analytical probes such as mass spectrometry and high-temperature gas chromatography. These field deposits consisted predominantly of polycyclic tetracarboxylic ARN acids. Presence of ARN acids was also validated in South American crude oils. Furthermore, low molecular weight ARN acids with a C-70-C-72 hydrocarbon skeleton were identified in all the calcium naphthenate field deposits as well as in the crude oil samples. Another interesting observation reported is the striking resemblance in the molecular signature of ARN acids from South America to those from West Africa.