Program obfuscation protects a program's intellectual property rights and vulnerabilities by making it unreadable and hardening program analysis. However, obfuscation typically adds size and complexity to programs, resulting in performance overhead. Fortunately. opaque predicates, which are the conditional expressions always evaluated to be true or always false, reduce the overhead by ensuring that the inserted dummy code is never executed. Furthermore, when combined with other forms of obfuscation such as MBA obfuscation, opaque predicates have been found to efficiently defeat existing SMT-based analysis methods. However, new program analysis techniques have recently emerging that can simplify more obfuscation, which suggests that opaque predicate-based obfuscation may no longer be robust enough. In this paper, we introduce a novel opaque predicate classification, taking into account robustness against various deobfuscation techniques. According to this proposed classification, we assess real-world obfuscation results produced by popular obfuscation tools.