For a d -dimensional array of random variables { X n , n ∈ ℤ + d } such that { | X n | p , n ∈ ℤ + d } is uniformly integrable for some 0 < p < 2 , the L p -convergence is established for the sums ( 1 / | n | 1 / p ) ( ∑ j ≺ n ( X j − a j ) ) , where a j = 0 if 0 < p < 1 , and a j = E X j if 1 ≤ p < 2 .