The doctrine of impracticability in the common law of contracts excuses performance of a duty, where that duty has become unfeasibly difficult or expensive for the party who was to perform.
Impracticability is similar in some respects to the doctrine of impossibility because it is triggered by the occurrence of a condition which prevents one party from fulfilling the contract. The major difference between the two doctrines is that while impossibility excuses performance where the contractual duty cannot physically be performed, the doctrine of impracticability comes into play where performance is still physically possible, but would be very burdensome for the party whose performance is due. Thus, impossibility is an objective condition, whereas impracticability is a subjective condition for a court to determine.
Typically, the test U.S. courts use for impracticability is as follows (with a few variations among different jurisdictions):
- There must be an occurrence of a condition, the nonoccurrence of which was a basic assumption of the contract,
- The occurrence must make performance extremely expensive or difficult
- This difficulty was not anticipated by the parties to the contract (note: some jurisdictions require that there be no measure within the contract itself to allocate risk between the parties)
Restatement of Contracts 
Section 261 of the Restatement (Second) of Contracts does not explicitly define the scope of what is considered impracticable, as it is a fairly subjective and fact-intensive test for the courts. Generally, courts do not consider events such as an increase in price or costs beyond a normal range to allow for discharge of duties on grounds of impracticability, as such events are normally foreseeable risks of fixed-price contracts.
Uniform Commercial Code 
Section 2-615 of the Uniform Commercial Code deals with impracticability in the context of sales of goods, and introduces some additional constraints on the parties. A party whose ability to perform his obligations has only been partially affected must allocate production and delivery among his customers in a manner which is fair and reasonable, affording each of them with partial performance, and must notify all purchasers that there will be delay, partial delivery, or non-delivery. This is similar in some respects to the doctrine of general average in admiralty law.
According to note 4 under UCC 2-615, increased cost alone does not excuse performance unless the rise in cost is due to some unforeseen contingency which alters the nature of performance. It further explains that a change in market conditions resulting a rise or drop in prices is not sufficient to claim impracticability because the parties assumed that risk when the contract was made. The comments indicate that contingencies such as war, embargo, crop failures, or a failure of a major source of supply that causes the market change or prevents a seller from obtaining supplies necessary for his performance would justify a claim of impracticability.
See also 
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Fri, 17 May 2013 22:09:22 -0700
You see, the subconscious idea may have been to get rid of my paunch, by beating to death—with the impracticability of a deep self-reflective bent—its repercussions, both the bad and the ugly. In other words, duly acknowledging the greatest gift god ...
Thu, 16 May 2013 05:34:50 -0700
Some common operational errors that are “small but pervasive” might fit under the final regulations' sections addressing administrative impracticability or disputed payments and refusals to pay relief, he said. Overpayment errors do not necessarily ...
Project Syndicate (blog)
Fri, 17 May 2013 03:31:34 -0700
With regards to the economic sociology -- the systems theorist Niklas Luhmann said that “variable prices make all economic behaviour a risk … any effort to achieve rationality shifts the centre of gravity towards impracticability, thus condemning ...
Fri, 17 May 2013 13:51:11 -0700
The two counts most intimately making this pitch are for reformation and impracticability. The former is a classic theory (and one notoriously ground into the minds of first year law students) whereby a court recognizes that an otherwise-valid contract ...
Bangor Daily News
Wed, 15 May 2013 08:00:30 -0700
Clearly the governor is not helping the budget process — both in terms of his tone, the impracticability of his budget proposals and his inability so far to adapt those proposals. Unfortunately, the Legislature already experienced its own rumblings of ...
Wed, 15 May 2013 07:31:19 -0700
It is not difficult to see the futility and impracticability of such national tasks. Given the challenges of governing an amalgam state and the tendency of such multi-national state to be prone to conflicts, several scholars have argued that when the ...
Linex Legal (registration) (press release)
Thu, 23 May 2013 14:38:45 -0700
However, as this date is not realistic and different Health Care Industry associations have raised its impracticability, a second date, 01 October 2013, has been recommended for the publication of these disclosures on the National Medical Association ...
Linex Legal (registration) (press release)
Mon, 20 May 2013 13:39:13 -0700
Form HC-1 Registration Statements and amendments thereto must be filed electronically by the insurer, unless the Superintendent grants an exemption based upon undue hardship, impracticability, or good cause. Written requests for an exemption must be ...
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