Large language models (LLMs) deployed in safety-critical settings must resist adversarial inputs designed to elicit harmful outputs. We present a systematic empirical evaluation of five adversarial jailbreaking attack families---direct requests, roleplay-based jailbreaking, hypothetical framing, instruction override, and obfuscation---across seven open-weight and API-accessible LLMs: Llama-3-8B, Llama-3.1-8B, Llama-3.2-3B, Mistral-7B, Qwen2.5-7B, Gemma2-9B, and Phi-4-14B. We further evaluate four defense mechanisms: keyword blacklisting, self-reminder prompting, paraphrase-based sanitization, and perplexity-based filtering against the two most vulnerable models. Our results reveal that obfuscation attacks achieve a mean attack success rate (ASR) of 54.3% across all models and constitute the most transferable adversarial vector, bypassing every evaluated model with nonzero success. We find that model size does not predict adversarial robustness (Spearman r=-0.57, p=0.18), and that models within the same architecture family exhibit dramatically different vulnerability profiles. Self-reminder prompting achieves the most consistent defense, reducing ASR from 44% to 10% on Mistral-7B and from 48% to 5% on Llama-3.1-8B with zero false positives and no additional inference cost. Our code and datasets are publicly available at https://github.com/Mdniloykhan/jailbreak-eval-7llms.

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