Few techniques for obtaining concurrent zero-knowledge exist; all require a complex and subtle analysis. We provide an arguably simpler and more general analysis of the oblivious simulation technique of Kilian and Petrank (STOC'01) while achieving the same bounds as Prabhakaran, Rosen and Sahai (FOCS'02). Using this analysis, and relying on tools recently developed by Ong and Vadhan (Eurocrypt'07, TCC'08) we are able to establish the following \emph{unconditional} results: \begin{itemize} \item every language in NP which has a ZK proof (resp. ZK argument, statistical ZK argument) also has a black-box concurrent ZK proof (resp. ZK argument, statistical ZK argument). \item every languge which has a statistical ZK proof also has an $\omega(\log n)$-round black-box concurrent statistical ZK proof. \end{itemize}