1. Straight-chain alkanes, when added to diesel fuel in amounts of 5% or more, harm the low-temperature characteristics of the fuel. The presence of these hydrocarbons will produce sharp increases in the cloud point, filterability temperature, and solid point of diesel fuels, and it is found that these three temperatures tend to converge when the n-alkanes are present. 2. The most effective pour-depressant additives are those containing such structural elements as an ester group in an aliphatic chain with olefinic bonds. The total molecular weight of such additives must be several times the molecular weight of the diesel fuel. 3. A given pour-depressant additive manifests identical effectiveness in fuels of a given hydrocarbon composition, including fuels with similar contents of n-alkanes.