We have already explained the concept of OI and strike price above. As mentioned earlier, retail investors generally take the long position and institutions short the option contracts. Strike with highest Put OI indicates the price level at which institutions have sold/written a lot of put option contracts. Thus, it means that they expect price to not fall below this level. For example, if Rs.7200 represents the strike with highest put OI for Maruti, then it means that institutions expect the price to not fall below Rs.7200.