Susta is oil-based testosterone blend. Sustanon is an injectable steroid with 4 testosterone esters: propionate (30mg), phenylpropionate (60mg), isocaproate (60mg), decanoate (100mg). Esters create a depot on the spot of administration, and from within the muscles the hormone is released in sustained manner. The role of esters is basically to make the synthetic hormones that resist immediate metabolism. Because of esters, the hormones are released steadily to Prevent fluctuation in blood levels. The longer and the heavier the ester attached, the longer the active life of the steroid.