How can I tell if an oil is refined or partially hydrogenated?

The short version: you can tell by reading the ingredient list and the Nutrition Facts panel, not by looking at the bottle.

The only reliable way to tell if an oil is partially hydrogenated is to check the ingredient list for the phrase "partially hydrogenated" followed by the oil name. That is a legal requirement in the US and many other countries. The Nutrition Facts panel will show "Trans Fat" grams per serving, but a loophole allows anything under 0.5 grams per serving to be rounded down to zero, so a product can contain small amounts of trans fat and still say 0 g on the label [1]. The evidence shows that by 2013, only about 14% of branded spreads in the US still contained partially hydrogenated vegetable oil, down sharply from earlier years [1]. A product that lists "hydrogenated" without "partially" is fully hydrogenated, which produces mostly stearic acid, not trans fats.

Refined oil is harder to spot from the label alone. Almost every clear, neutral-tasting vegetable oil on the shelf is refined: it has been through degumming, neutralization, bleaching, and deodorization at high temperatures (around 240–250 °C) [2][4]. The label will not say "refined" because that is the default. You can infer it: if the oil is pale, odorless, and has a high smoke point, it is almost certainly refined. Cold-pressed or unrefined oils will say "cold-pressed," "unrefined," or "virgin" on the label, and they will have color, flavor, and a lower smoke point. The refining process strips out most of the natural tocopherols (vitamin E) and phytosterols [3], so a refined oil has lost much of what made the original seed or fruit beneficial.

My call: read the ingredient list for "partially hydrogenated" to catch trans fats. Assume any clear, odorless oil is refined. Choose cold-pressed or unrefined oils to keep the natural protective compounds. Confidence: high on the label rules for partial hydrogenation, moderate on the nutritional difference between refined and unrefined oils (the evidence shows the chemical losses but does not test long-term health outcomes from those losses).