Four classes of three-dimensional quadratic algebra of the type [Q(0), Q(+/
-)] = +/-Q(+/-), [Q(+), Q(-)] = aQ(0)(2) + bQ(0) + c, where (a, b, c) are c
onstants or central elements of the algebra, are constructed using a genera
lization of the well known two-mode bosonic realizations of su(2) and su(1,
1). The resulting matrix representations and single variable differential
operator realizations are obtained. Some remarks on the mathematical and ph
ysical relevance of such algebras are given.