This is the third paper from a series of articles on governing of different types of transactions in Bulgarian farming applying the framework of New Institutional and Transaction Cost Economics. It is based on a large scale microeconomic data from 194 typical commercial farms of different sizes (small, middle-size, big) and types (individual, family and group farms; cooperatives, agrofirms) from all regions of the country. This study concentrate on factors and modes for organization of inputs supply in Bulgarian farms. Different governing forms (internal production, own cooperative, member-organization, market contragent) for major types of current (chemicals, seeds, forage) and long term (buildings, machinery, livestock) inputs supply in farms of different types and sizes has been determined. Microeconomic factors responsible for various organizational and contract choices for input supply (buying, leasing, internal procurment) have been specified. Dominant governing modes have been explained by comparative advantages for saving on transacting costs (for finding partners and needed material assets, contracting, contract enforcement and disputing, renewal of contracts etc). Extension (optimization) of farm size through some mode of input supply is undertaken only if it is less expensive comparing to other forms for farm enlargement (e.g. land supply, labor supply, service supply, vertical integration etc). Transaction costs economizing framework has been used through analysis of: frequency of transactions between same partners (always the same partner, usually same partner, different suppliers, every time and season a different partner); reasons for choosing the supplier (the best prices, postponed payments, good reputation of supplier, providing supply on farm, lack of other suppliers, high quality, tradition, high confidence in the supplier, additional benefits); price type (based on market price, negotiated every time, fixed for a long period); interlinked relations (supplier buy farm output, suppliers assist ...
