Getting a consensus  may be impossible.  For example, you yourself would likely have commented to someone "Wow, the lanes are dry tonight", and the other person would say, "They're not all that dry..." ....and so on. In other words, the conditions will vary from each bowler and bowling style.

Having said that, there is probably a way of measuring the amount of oil on the lanes and there is probably a range that describes the three catagories:- Oily, Medium and Dry, - Oily ranges from 100 - 67; Medium ranges from 66 - 34, and dry ranges from 33 - 0. There would not be much difference between 34 and 33 for example. 

 

There was a old thread on here where they asked about how many units of oil was considered Heavy, Medium and Light.

Here's some info I looked it up at the time. if it helps

First what is a unit of oil defined as, I found this in a 04/05 Spec. manual. (It's in the "Computerized Lane Inspection Program Manual" you can find it on bowl.com)

"A "unit" of oil is defined by the American Bowling Congress (ABC) and Women's International Bowling Congress (WIBC) as 0.0167 cubic centimeters of oil evenly spread over a 1 sq. ft. surface, which equates to a film of oil about 7 millionths of an inch thick."

Now in In USBowler Magazine Vol.2, No.3 Spring 2007 Page 12 Coach's Corner They have a article "Everything you wanted to know about lane conditions" In it they say,

Example: a piece of typing paper is about 400 units thick.
(.000007*400=.0028"  A 16# bond paper is .0032" thick so that's pretty close.)

"A layer of oil 100-plus units would be considered "Heavy oil" and anything less then 50 units probably would be "Light oil".

Now in from other source's Oil, Medium and Dry is looked at in terms of length.

In the book "Revolutions 2" they define it this way,

Oil (long oil) were lanes oiled 35 to 45 feet.
Med. were lanes oiled 25 to 35 feet.
Dry (very short oil) was 18 to 25 feet.

Now in In USBowler Magazine Vol.2, No.3 Spring 2007 Page 12 Coach's Corner They have a article "Everything you wanted to know about lane conditions" In it they show it as,

Long oil as 40 feet or longer
Medium oil as 35' to 45' feet or more
Short oil 35 feet or less

Now in Bowling This Month magazine they rate ball's for Oil, Medium and Dry, the current issue is showing these patterns being used.

Oily is a 44' oil (High Street)
Medium 41' oil (Main Street)
Dry 38' oil (Easy Street)

High Street, Main Street and Easy Street, These are the Kegel Navigation Recreation Series of patterns. you can see them here.
http://www.kegel.net/patternlibrary/default.asp

Now for a comment it's not how much oil on the lane, but where it's at. Pattern's can be adjusted to make short ones appear long and long ones appear short.

Heres a quote from a article called- "Lane Pattern Basics: An Overview of Blend, Taper & Application".
Click here for the article

"the overall volume of the shot probably has the least affect, as the length that the conditioner is applied can make the "volume" almost meaningless."

When it comes to Oil and Oil patterns there are many factor's that come into play about lane condition's and how to play them. The amount of oil is one of the smaller factor's involved.

I would pretty much agree with Jeff's position.  Being that proprietor's don't put out that and dumb it down so the least common denominator skilled bowler can strike that puts the other 50% to 70% at a disadvantage but good bowlers adjust.
 

In addition to that, you also have to be a practicing Medium
 

Probably not going to happen, because as was stated earlier the actual amount of oil doesn't have as large of an impact on the categorization of the oil pattern when compared to something such as lane surface. We use the Kegel High Street pattern as our base house shot and it's lane dependent on how the shot is classified. Unfortunately, it's also not as simple as the high or low side hooking more than one another.