C. F. Keil and Franz Delitzsch on Genesis 26:12

Gen 26:12

Isaac’s Increasing Wealth. - As Isaac had experienced the promised protection (“I will be with thee,” Gen 26:3) in the safety of his wife, so did he received while in Gerar the promised blessing. He sowed and received in that year “a hundred measures,” i.e., a hundred-fold return. This was an unusual blessing, as the yield even in very fertile regions is not generally greater than from twenty-five to fifty-fold (Niebuhr and Burckhardt), and it is only in the Ruhbe, that small and most fruitful plain of Syria, that wheat yields on an average eighty, and barley a hundred-fold. Agriculture is still practised by the Bedouins, as well as grazing (Robinson, Pal. i. 77, and Seetzen); so that Isaac’s sowing was no proof that he had been stimulated by the promise of Jehovah to take up a settled abode in the promised land.