Learn Russian: При выполнении этой работы мы часто ошибаемся. - When doing this work, we often make mistakes.

Using при + Prepositional case with a verbal noun (like выполнение, meaning 'execution' or 'performing') is a concise way to express a simultaneous circumstance. While когда мы выполняем is perfectly fine for everyday speech, при выполнении sounds slightly more formal and professional, translating closer to 'during the performance of'.

Why is этой работы in the Genitive case here?

It acts as the object of the verbal noun выполнении. When an action verb that normally takes the Accusative case (like выполнять работу) is turned into a noun, its object is always placed in the Genitive case (выполнение работы). This is exactly equivalent to saying 'the doing OF the work' in English.

Could I use the gerund выполняя instead to say 'when doing'?

Yes, you can! Выполняя эту работу, мы часто ошибаемся is a very natural alternative. The difference is mostly stylistic: the gerund выполняя focuses on the action itself, while при выполнении acts as a noun phrase and leans toward a slightly more formal, instructional, or technical register.

I see ошибаемся ends in the reflexive particle -ся. Can I use it without the -ся?