According to both the Merck Index and the U.S. Pharmacoepia, the three major testosterone esters (propionate, cypionate, enanthate) and nandrolone decanoate are considered to be "soluble" in oil and "freely soluble" in alcohol. Though it doesn't seem like it, the USP has strict definitions for these terms.
Soluble: Between 10 to 30 parts of the solvent (in this case, oil) are required to dissolve one part of the solute (the steroid).
Freely Soluble: Between 1 and 10 parts of the solvent are required to dissolve one part of the solute.
The above ratios are weight-to-weight.
Vegetable oil has an approximate density of 900 mg/ml at room temperature. That means, according to the USP, that only about 90 mg maximum can be dissolved in 1 ml of oil. The longer the ester, the closer you get to the 90 mg. This has to do with chemical polarity, which I'm going to get into. Doesn't seem right, does it? Well, read on.
Alcohol, for the sake of argument, has a density of about 1000 mg/ml (similar to that of pure water). According to the USP, up to 1000 mg of the steroid can be dissolved in 1 ml of alcohol!
Commonly, the oily mixture used for injections contains 90% cottonseed (or some other vegetable-based) oil and 10% alcohol by volume. So, using the basis from the USP, at most you could have 90 mg (from the oil) and 100 mg (from the alcohol) to provide a mixture of 190 mg/ml. Yet, we know it's possible to reach concentrations much higher than that!
Why? Oil and alcohol work synergistically to increase the solubility of an organic solution, increasing the concentration two- or three-fold! Therefore, it's very possible to make a solution of 400 mg/ml testosterone ester mixtures like the new Denkall product or 300 mg/ml nandrolone decanoate like the Ttokkyo product.
