The grantee, at all times during the existence of this franchise, shall use its best efforts to obtain and supply a continuous, sufficient and adequate quantity of gas for use by said city and its inhabitants, provided; however, that grantee shall in nowise be liable to said city or to its inhabitants because of the interruption or discontinuance of the supply of gas by causes beyond the reasonable control of grantee. (1983 Code § 13.02.030)