speculate

Speculation can sometimes drive securities prices away from their intrinsic value, either becoming overpriced during a buying frenzy or becoming underpriced during a huge sell-off. Although speculators sometimes get a bad rap in the press for this reason, they are a crucial lubricant to the markets, particularly the commodities markets. Although they don't want to physically possess any of the commodities they're trading (that is, they don't really want a truckload of rice delivered to their door), their trading activity brings liquidity to the market, which in turn provides stability and efficiency to those markets.

It is important to note, however, that speculators are generally bigger risk takers than other investors. They are more likely than other investors to use leverage, and as such can suffer huge losses alongside huge gains.