This thesis studies the operating behaviour of the manual unpaced lines, which are the most important of the flow lines' systems. The lines examined are unbalanced and six types of imbalance are considered, namely, the imbalances of mean service times, coefficients of variation (Covars), buffers'capacities, means and Covars, means and buffers, and Covars and buffers. It is argued that the deep understanding of the behavioural characteristics of such lines, contributes towards the achievement of practical solutions to many of their problems. The lines are simulated under both steady and non-steady states conditions, with positively skewed weibull work times distributions, different values of line length (N), buffer capacity (B), degree of imbalance (DI), and pattern of imbalance, utilizing full factorial designs. The data are subjected to the analysis of variance, multiple regression, multiple comparisons with control, pairwise comparisons, canonical correlation, and utilitv analysis A simple utility approach is also explored briefly. Some of the important conclusions for all the unbalanced lines' investigations are: (1) At least one unbalanced pattern generates superior idle time (I) and/or mean buffer level (ABL), over those of a balanced line. The superiority in I decreases as DI rises, whereas the advantage in ABL reduces as DI is decreased.(2) The DI of the best unbalanced pattern can substantially or moderately be increased and still yields approximately equal I to that of a balanced configuration.(3) If a line is unbalanced in the wrong direction, significantly inferior performance to that of a balanced design will result.(4) The unbalanced patterns' I tends to decrease, when N and DI reduce and B increases, while ABL falls directly with B.(5) The I's transient size increases as N and B become higher and DI increases, while the ABL's transient size rises whenever B reduces.