The nonnegativity of the determinant of the partial transpose of a two-qubit (4×4) density matrix (ρ) is both a necessary and sufficient condition for the separability of ρ. While the determinant of ρ itself is restricted to the interval [0, 1 256 ], the determinant of the partial transpose (|ρ P T |) can range over [− 1 16 , 1 256 ], with negative values corresponding to entangled states. We report here the exact values of the first nine moments of the probability distribution of |ρ P T | over this interval, with respect to the Hilbert-Schmidt (metric volume element) measure on the nine-dimensional convex set of real two-qubit density matrices. Rational functions C 2j (m), yielding the coefficients of the 2j-th power of even polynomials occurring at intermediate steps in our derivation of the m-th moment, emerge. These functions possess poles at finite series of consecutive half-integers (m = − 3 2 , − 1 2 , . . . , 2j−1 2 ), and certain (trivial) roots at finite series of consecutive natural numbers (m = 0, 1, . . .). Additionally, the (nontrivial) dominant roots of C 2j (m) approach the same halfinteger values (m = 2j−1 2 , 2j−3 2 , . . .), as j increases. The first two moments (mean and variance) found-when employed in the one-sided Chebyshev inequality-give an upper bound of 30397 34749 ≈ 0.874759 on the separability probability of real two-qubit density matrices. We are able to report general formulas for the m-th moment of the Hilbert-Schmidt probability distribution of |ρ| over [0, 1 256 ], in the real, complex and quaternionic two-qubit cases.