The article is devoted to one of the most common translation problems in the sphere of law, namely finding the adequate equivalents in vocabulary, especially it concerns foreign terminology, in grammar and in text structure.

While it is well-known that equivalence is one of the key concepts in translation, the research on practical applications of this principle in different professional spheres is still limited. With the rise of the interest to the machine translation, the special attention to the most common translation problems in the sphere of law can contribute to the overall understanding of the translation process. The methodological approach taken in this study is a mixed methodology based on comparative, structural, socio-linguistic and socio-cultural aspects of translation. The material presented in the article is based on the original contracts developed in English and Russian for the major oil and gas projects to be implemented in Russia 2006-2009. The examples of vocabulary, grammar and text structures equivalents can show the reasons for emergence of the main translation difficulties - polysemantic structure of some terms, absence of concept in either language, dependence of the meaning of the term on the context, idiomatic expressions, historically established traditions in legal text formation – emphasizing the idea that equivalence principle should be considered as a priority when translating contractual documentation.