Usage patterns
〈物〉に投機するto speculate in (something, e.g. stocks, land)
He speculated in land and lost a fortune.
投機に走るto turn to speculation (often recklessly)
Amid the recession, many companies turned to speculation.
投機の対象となるto become an object/target of speculation
That land became a target of speculation.
投機的な〈物〉a speculative (deal, investment, etc.)
He got involved in a speculative deal.