Such searches are conducted to locate prior patents or other publications disclosing the closest prior technology to a given searched feature of the invention.  As a prior publication or patent anywhere in the world that describes the feature (or in view of which the feature is obvious) precludes patent protection for the feature, theoretically one should search in all of the world's patent offices and libraries.  But the cost of a comprehensive preliminary patentability search can quickly exceed the cost of preparing and filing a patent application.  So, unless it is necessary to protect the invention worldwide, such preliminary search is usually restricted to the most obvious classifications of relevant patents and published literature that may be found in a particular patent office, limiting the expense to an acceptable level.  We generally select the United States Patent and Trademark Office, as it contains a relatively large volume of accessible information, and most Canadian inventors wish to obtain a US patent.  Such limited search is usually a good preliminary indicator whether the invention is likely to be patentable, and facilitates the drafting of the patent specification to distinguish the invention from what was previously known.  A preliminary patentability search is best done by a trained searcher who can speak to the Examiners in the Patent Office with a view to making sure that the most pertinent classifications of subject matter are searched.  The cost varies as to subject-matter and the number of patentable characteristics of the invention that must be searched, but typical fees and disbursements for the searching of one inventive feature run from about $2,000 (occasionally less) to about $2,500.  Searching other potentially patentable features typically increases the cost by at least about $500 per feature searched.