Craig L. Blomberg, "When is a Parallel Really a Parallel? A Test Case: The Lucan Parables," WTJ 46 (1984): 78-103. ***
Few New Testament scholars would dispute that literary dependence of some sort is required to account for the high degree of similarity between eight parables in Luke and their Synoptic parallels, but five other Lukan parables (12:35-38; 14:16-24; 14:5; 19:11-27; and 15:4-7) and their Synoptic parallels are better explained as having been spoken in more than one form on separate occasions.
A well-written and conservative piece which in the end is not altogether convincing.