Legality in California
Polymarket offers US event contracts through its CFTC-licensed exchange and clearing house and is available across all 50 states on iPhone. ProphetX holds its own CFTC DCM and DCO licences and went nationwide in 2026 on every device. Both are federally regulated, so California residents 21 and over can use either.
Markets and coverage
Polymarket lists politics, culture, news and sports, and its high-volume contracts are the deepest in the US. ProphetX is sports only: NFL, NBA, MLB, NHL, college football, soccer and combat sports. If you want the LA mayor's race or an awards market, that is Polymarket. If your entire watchlist is games, ProphetX is purpose-built for it.
Pricing & fees
ProphetX carries no house margin because positions are matched trader to trader, with a small commission on winners only. Polymarket's US pricing is competitive and its spreads on liquid markets are the tightest available, which often matters more than the fee line on a large position. On thin sports contracts, the peer-to-peer book on ProphetX can fill better than a wide quote elsewhere.
User experience
Polymarket's US product is a polished iPhone app with charts, news context and a social feed, but there is no US Android app and no desktop trading. ProphetX runs on iPhone, Android and web with a league-first sports layout. Both verify identity at signup and fund by debit card or bank transfer.
Who should use which
Use Polymarket if you have an iPhone and want depth plus politics and culture in one account. Use ProphetX if you are on Android or desktop, or if sports is the only thing you trade and you want peer-to-peer pricing. Holding both covers every market type and every device.