1. Distribución de S, V y Ni en crudos y asfaltenos de los campos Mara y Mara Oeste, Cuenca del Lago de Maracaibo, Venezuela;López;Interciencia,1991
2. Use of trace elements for classification of crude oils into families—examples for Alberta, Canada;Hitchon;AAPG Bull,1984
3. Distribution of trace elements in crude oils from Southern Germany;Ellrich;Chem Geol,1985
4. Distribución de V, Ni, Zn, Mo, Ca, K, Fe y Cu en los crudos de la Cuenca Oriental de Venezuela;Simoza;Memorias VI Congreso Geológico Venezolano,1985
5. Classification of some New Zealand crude oils and condensates by means of their trace elements contents;Frankenberger;Appl Geochem,1994