Perhaps you have noticed an advertisement that Shell runs on gas reserves. It reads: “Yes, the world’s remaining gas reserves are getting harder to reach” (see here for the advertisement and here for the website). This statement always makes me smile, as it shows that many companies pay lip service to economics when it comes to communication about environmental issues. This statement is both true and false depending on what one means by “gas reserves.” The crucial word missing in the ad is “known” (in the way Austrian economists use the word).
On the one hand, the statement has been true from the first day gas reserves have been exploited by mankind. At any moment among known gas fields (including the known areas where gas is likely to be located), companies will exploit easy to reach gas reserves first and harder ones later. Thus, the fact that the world’s remaining known gas reserves are getting harder to reach has always been true, it is not a consequence of gas running out.
On the other, the statement is false if one considers that some gas reserves may be truly unknown in their location (people truly don’t suspect there could be gas in a given location or that it could be easy-to-reach), but if discovered it could be easy to exploit (at least easier than others currently exploited). If my knowledge is correct, it has been the case with the discovery in 1969 of the giant Maui gas field in New Zealand, which is located in the Tasman Sea off the Taranaki Coast (with its beautiful volcano).