Proof by a preponderance of the evidence means probable not possible. Here, a taxi service sought a Certificate of Public Convenience and Necessity from the Public Utilities Commission so it could operate in Denver. Existing taxi companies objected, claiming another taxi service would cause oversupply in the market and not lead to robust competition. An ALJ concluded there was a significant “possibility” the objectors were right. The PUC affirmed, using “possibility” and “probability” interchangeably. The Court held that “probable” expresses higher confidence than “possible,” and is closer to “preponderance.” Thus, objectors must prove, and the PUC must clearly manifest an intent to apply a preponderance standard to find that a Certificate was not required, and issuing one would actually be detrimental. The PUC did not do so; the denial of the Certificate was reversed.