Continuous operation of  Ammonia and Urea plants is pre-requisite for achieving high operational efficiency. There are several causes of interruption in operation. These could be breakdown of plant and machinery, shortage of raw materials and utilities, labour problem and  other reasons like high inventory and natural calamity.  In order to address the problems, it is essential that causes of interruption are identified and their effect is quantified.  With this objective, FAI has been carrying out the analysis of downtime in ammonia and urea plants for several years. The data for planned downtime, forced downtime and on stream days were calculated and compared with the data of previous surveys. Factors responsible for loss of production due to problems in plant and equipments as well as external to plants are segregated and analyzed. A detailed analysis of each section of the plants has been done in regard to problems due to plant and equipments. The present study, tenth in series, evaluates data of 28 ammonia and 27urea plants for 2011-14 period for various causes of downtime. The paper presents the results of the study and identifies areas that need attention of plant management to further improve reliability and operational efficiencies of ammonia and urea plants.