How do I use AI deep research agents (ChatGPT, Gemini, Perplexity) to produce a market research report?

Deep research modes turn one well-written brief into a cited, analyst-style report by autonomously reading hundreds of sources over 5 to 30 minutes. The craft is in the brief: give the agent a persona, a scoped market, explicit exclusions, and the output format you want, then interrogate the citations rather than accepting the prose. Each tool has a personality: Perplexity is fastest with the cleanest citations, Gemini shows you its research plan before running, and ChatGPT goes deepest on analysis.

A quick orientation. The real value is below: resources worth your time, from people who've actually done it.