Gas has become so cheap that it can be substituted for coal as an electricity-generating fuel.

CNN: 'Peak oil' doomsayers proved wrong

Advocates admit that the only way coins can be substituted for paper is to remove the paper version from circulation.

FORBES: NO PEEPING WITHOUT PERMISSION

Bay scallops belong to the same family: They are much smaller, about half an inch, but can be substituted for sea scallops (use three bay scallops in place of one sea scallop).

NPR: Scallop Mango Tartlets: Sweet Start to the New Year

Though there are many more bonds than equities, they are far more homogenous, and thus can be relatively easily substituted for each other in portfolios.

ECONOMIST: E-bonds, licensed to kill

It will not take long, he claims, for the proceeds to be substituted or diverted to the government's preferred ends.

ECONOMIST: Taxation

With Kris Boyd a peripheral figure, thanks in part to the attentions of McLaughlin, he was substituted midway through the second half for Kyle Lafferty, rumoured to be attracting interest from Wolves.

BBC: Rangers 1-0 Hamilton

Rosicky was substituted at half-time in Arsenal's win and Wenger confirmed the midfielder could be out for a month.

BBC: Arsenal's Tomas Rosicky sidelined with groin injury

Since oil is easily substituted for natural gas in many industrial and electrical turbines, prices of the two commodities tend to be correlated (coal less so).

FORBES: The Prize