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A radio k -labeling of a graph G is an assignment of non-negative integers (labels) to the vertices of G such that the absolute value of the difference between the labels of any two distinct vertices u and v is not less than k + 1 − d (u , v) , where d (u , v) denotes the distance between u and v. The radio k -labeling number of G is the minimum span of a radio k -labeling of G. For a given set of integers D = { d 1 , d 2 , ... , d t } , the distance graph G (Z , D) , denoted also by D (d 1 , d 2 , ... , d t) , has the set of integers Z as its vertex set, while two distinct vertices i , j ∈ Z are adjacent in G (Z , D) if and only if | i − j | ∈ D. Radio k -labelings of three families of distance graphs are considered. Some improved theoretical lower and upper bounds on the radio k -labeling number are presented and some computer-based methods for computing radio k -labelings of these families of graphs are proposed. [ABSTRACT FROM AUTHOR]