Filling an OMR (Optical Mark Recognition) sheet correctly is crucial for accurate automated reading and data capture. One often overlooked but highly important factor is the colour and type of pen used to fill in the bubbles or response zones. This guide explains the reasoning behind colour choice and pen type, and offers clear instructions to help you avoid scanning errors.
The process of OMR scanning relies on detecting dark, well-defined marks that the software recognizes with high contrast. The colour of the pen mark plays a key role in this:
Darker colours like black and blue provide strong contrast against the white background of the OMR sheet, making them easier for the scanner to read.
Lighter colours such as red or green may appear as “grey” when converted during scanning, lowering detection accuracy and increasing risk of mis-read.
Additionally, certain colours carry meanings (for example red might be used by examiners, green by supervisors) which further supports the decision to restrict student marks to blue or black.
Therefore, when the instructions on an OMR sheet say “Use blue or black ballpoint pen”, this is not just a suggestion but a technical requirement for reliable scanning.
Here are the best practices you should follow when filling an OMR sheet:
Prefer black ball-point pen or blue ball-point pen unless your specific sheet instructs otherwise.
Avoid gel pens, fountain pens, marker pens or sketch pens — these can cause smudging, bleeding, or impressions that interfere with the scanner.
Make sure to fill the bubbles completely and darkly; a light or partial mark may be skipped or mis-read by the scanner.
Some exam bodies allow filling with pencil. In such cases use a dark HB or 2B pencil only, and ensure the sheet design is suited for pencil use (e.g., coloured sheet, larger bubbles).
If a pencil is used but the sheet was designed expecting pen marks, there is a higher risk of errors due to lighter marks or ghost outlines.
Using colours other than blue or black (such as red, green, orange) for filling response bubbles.
Using gel pens or fountain pens which may still be permissible in some cases but are prone to smudging and bleeding.
Filling with pencil when the sheet expects pen, or vice versa, without verifying instructions.
Not fully darkening the bubble, leaving partial marks, tick marks or crosses when full shading is required.
Overwriting or going outside the bubble area, or using too much ink and causing blotting.
Marking with a pen whose ink is too light, or using mixed colours or inconsistent pen types during the exam.
Most examination instructions for OMR sheets will include lines such as:
“Use only blue or black ball-point pen”
“Do not use gel/fountain/sketch pens” … “Do not use colours other than those specified.”
“Completely fill the circle; partial filling or tick marks not allowed.”
The reason this guideline exists goes beyond administrative convenience is rooted in the mechanics of how OMR systems work:
The software scans the sheet and looks for contrast between the mark (filled bubble) and the background/outline of the bubble. Dark pen marks create a strong readable signal.
Lighter colors or non-ballpoint pens often create inconsistent fill densities, smudges, ghost marks or bleed-through, all of which raise error-rate or manual correction workload.
By standardizing blue or black ballpoint pens, exam bodies simplify scanning thresholds, reduce manual intervention and improve throughput.
Here are steps to follow on exam day before you begin filling the OMR sheet:
Check instructions on the OMR sheet or question booklet to see if a specific pen colour/type is required.
Use a good ballpoint pen of acceptable colour (blue or black) that writes darkly and cleanly.
Ensure the pen is working properly — avoid starting with a pen whose ink is faint or streaky.
Fill each bubble completely and darkly, being sure not to scribble excessively or press so hard as to create holes.
Avoid corrections or white-out, unless permitted and documented.
Stick to one pen for the OMR sheet if possible, to maintain mark consistency.
Addmen Group Copyright 2025. All Rights Reserved.
