%0 Journal Article %T Existence and nonexistence of periodic solutions of n-vector differential equations of orders six and seven %A Victor F. Payne %A Haroon Oladipo Tejumola %J Electronic Journal of Differential Equations %D 2012 %I Texas State University %X In this article, we extend our earlier results and establish new ones on the existence and non-existence of periodic solutions for n-vector non-dissipative, nonlinear ordinary differential equations. Our results involve both the homogeneous and non-homogeneous cases. The setting for non-existence results of periodic solutions involves a suitably defined scalar function endowed with appropriate properties relative to each equation. But the framework for proving existence results is via the standard Leray-Schauder fixed-point technique whose central theme is the verification of a-priori bounded periodic solutions for a parameter-dependent system of equations. %K A priori bound %K Leray-Schauder fixed-point teorem %K parameter-dependent system %K periodic solution %U http://ejde.math.txstate.edu/Volumes/2012/97/abstr.html